I've been going through PC Hell for the last three weeks, apparently as a result of a memory upgrade. I eventually got everything running (After numerous reformats, reinstalls, etc.) but I was getting the infamous black screen a few seconds after loading a flight. I tried Microsoft's recommendations (clean reboot, lowering sound and video acceleration, reinstall Directx) but nothing worked. Even FS2002 had the same problem.
In the course of reverting back to the last time things worked, I removed the new memory module (a 512 MB DIMM) and put the two remaining 256 MB DIMM's back in their original slots. Naturally, FS2004 works perfectly now. I don't know what the problem is with the memory, but apparently some motherboards are choosy about what DIMM's go in what slots. In theory, any DIMM should work in any slot, as long as the number of pins matches, but reality and theory may not agree on this.
If you are having the Black Screen Blues, try experimenting with your RAM. Do you have DIMM's of varying sizes? Try removing any mis-matched modules. You might even try leaving only one DIMM in slot one. Performance may not be the best, but if you can at least run a flight in FS without the Black Screen, you may be on to the problem. The next step is to try out different combinations of DIMM's and slots. If you can';t find a combination that works, check your motherboard's manufacturer for a listing of compatible memory modules. The safest route may be to use the same size DIMM form the same manufacturer in each slot.
WinXP Home SP1
P4 2 gig
Via P4PB 400
512 MB DDR Ram PC2700
GeFroce Ti 4600