Here's how it works.
1st) you have the total potential tax you can collect from all of your planets. I don't know that there is anywhere that reports what this number is, but it is based near as I can tell on the population and planet quality of each planet modified by Econ bonuses for that planet and glactic wide bonuses.
2d) you have your tax rate which is the % of this total amount you actually get. Thing is moveing the slider has two effects. It increases the % of the total as you move it to the right, but DECREASES the total. This represents more and more tax evasion as rates become oppressive. At some point you're getting a higher percentage of a lower total so the amount you actually collect goes down. Play with the slider to make sure you've got it set to the sweet spot to maximize your actual collection (you might have to lower it below the sweet spot if you run into morale problems...taxes also piss people off).
3rd) The amount you collect from taxes is then reduced by the spending slider. How much of what you collect are you actually going to spend and how much are you going to save. Whatever you choose to spend drops to the project sliders (social, military, research). Whatever you choose to spend goes over to the right side of the screen
4th) The amount choose to save is reduced by maintenance costs. Buildings (social projects) have maintenance costs as to ships. If you've built buildings and ships faster than you've increased your economy you may not have any money left after paying this maintenance. In fact your savings rate might go negative. You can see these on the upper right of the econ screen. Whatever you spend on projects also gets converted into bc and shows up on the right side of the screen.
5th) If your maintenance is REALLY high you might be in a position where even if you save EVERYTHING (spending to 0%) you still don't have enough in taxes to pay maintenance. This usually happens late in the game when a recession even hits or you lose a big Econ boosting starship or tax wealthy planet in a war.
6th) Whatever you're spending on social or military projects then gets divided among all of your planets (even planets which aren't currently building either of those, which is a point of contention among some). If this amount has dwindled through the above steps to a point where it is too small you will get the No Resources notice.
7th) This is the BIGGIE. I am guessing this is the one that's killing you because I can't imagine how it would be possible to build enough high maintenance items to cripple your income that early in the game. LEASES. Leases can be very useful, they can also kill you. When you go into a planetary building screen you select what projects you want to build and it will tell you how long to build them...this represents building them new from scratch. If instead, you click on the Purchase button you can intantly build the project (this basically represents the government contracting out the project to some civilian contractor). You will be presented with several options, most of which involve paying a certain number of BC per turn for X turns. This is treated exactly like Maintenance above (you can't choose not to pay it) and also shows up on the right side of the econ screen. I'm guessing you entered into ALOT of these leases and are paying through the nose...like paying interest on a giant national debt. That's the only think I can think of that would effect you this way this early.
So...what to do about it.
Option 1: Find a way to increase your tax rate. In the long run this is IMO the best path to victory, but over the short run isn't going to help you because you have to spend money to make money. But, employing this strategy can help you avoid this situation in future games.
a) Build Econ Boosters (Banking Centers, stock markets etc) on EVERY decent planet you have.

Build starbases on Econ resources and upgrade the mining as much as you can using Constructors.
c) Learn to master the art of morale. Build too many morale boosters and you just increase your maintenance for little gain. But build the right amount (less is needed on high PQ planets) and you'll keep planetary morale up. High planetary morale means more taxes from that planet. Enough High Planet morales equates to a higher approval rating which allows you to support a higher tax rate before people get pissed.
Option 2: Find additional sources of income OTHER than taxes. This is a useful short term strategy. You should be able to dig yourself out of debt with this one.
a) Trade. Trade is very very important. By mid game Taxes will NOT cover you're income needs even if you're doing well with Option 1 above. At least they will not cover them AND leave you enough money to stay ahead of the tech race and maintain a sizeable fleet. Build frieghters and send them to nearby planets this will give you trade quickly. Then build freighters and send them to the farthest planets you can reach. When they arrive kill the short route and build the long one...its worth more. Trade also has major political repurcussions so choose your tradeing partners wisely. Research Trade Route increaseing tech to increase your routes and hense your possible income.

Build starbases in sectors where your frieghters pass through and upgrade the trading post facilities on them with constructors. This will allow you to collect more bang from each route.
c) Sell tech, ships, or if necessary planets to other races. If you're really in the hole, this is the only option that doesn't require spending money first. Find a race, preferably one that likes you and offer them some tech. I AVOID selling diplomacy tech (because it just makes this harder in the future) or military tech except outdated stuff, but you might not have that luxury). Try to get several different races (minors are ideal for this) paying you 100-250...maybe even as high as 400 bc per turn for several turns (I once had the Altarians paying me 500bc/turn for 50 turns but that was because I was exterminating them). Use this cash to stabilize your budget.
Option 3: Scrap projects. Kill the maintenance requirements by getting rid of stuff that you don't need. Old starships that couldn't stand up to an enemy attack anyway...kill em. Superexpensive morale boosting projects on high PQ planets with low population...you don't need em to keep em happy, scrap em. Expensive econ and production boosters on low pop low PQ planets. No matter how much you boost these lower PQ planets they're never going to produce much in taxes or production anyway...you're likely paying more in maintenance than your getting from them. Scrap that stuff. Influence boosters in worlds no where near an enemy. Embassies and cultural centers and other things like that. If you have 3000 influence in a sector and the aliens have 100, you're paying maintenance on a lot of unnecessary over kill. Scrap 'em (but wait a few turns in between to monitor the influence effect. Influence ripples, so check the border areas to make sure they aren't being weakened too much first.
That's my Econ management primer. I've lost ALOT of games. NEVER because I didn't have enough money.