To state the obvious it has to be a problem with one of the following - Fuel (pumps, filter, fuel lines, regulator or injectors), Air (filter, air box, supercharger, intercooler or throttle body ) or Spark (coil, distributor, leads or spark plugs).
-The more accurate a desciption of exactly how the car is behaving often makes it easier to narrow down the problem!!
How is it driving across the board? Is it a complete lack of power or intermitent.
Have you got a lack of power throughout the whole rev range or just some of it?
Does it struggle to get up to the higher revs when stationary?
How does it sound under load and revving freely?
Etc etc..
Some suggestions,,
Is there air leaking from any of the pipes including the intercooler, exhaust and manifold?
Is there enough fuel to the engine, any fuel leaks at the back of the car (ie smell of fuel by the pumps) or blocked lines maybe?
Do the HT leads or ditributor look worn?
Are all the connectors plugged in around the engine bay and bulk head...
Before concentrating on any one component just stop and try and go through the car logically, fuel air spark, part by part to see if there is anything that might be easily missed and is actually quite obvious. It might not be some thing that you need to be an expert mechanic to spot. Hope this helps a little - good luck