System specs are:
Mobo: Foxconn C51XEM2AA- 8EKRS2H Socket AM2 NVIDIA nForce 590 SLI
CPU: AMD Athlon 64 X2 3800+ Windsor 2.0GHz 2 x 512KB L2 Cache Socket AM2
Gfx Cards: Dual XFX GeForce 7600GS 256MB's in SLI
HD: Seagate Barracuda 7200 RPM 320gig SATA
Sound card: CHAINTECH AV-710
PSU:XCLIO GOODPOWER 500W

I used to use :
Corsair XMS2 2 x 512MB 240-Pin SDRAM DDR2 800 (PC2 6400)
however it was just my birthday and i recieved some money so I went out and bought:
Corsair XMS2 2x 1024mb 240-Pin SDRAM DDR2 800 (PC2 6400C4)
The only difference between the two ram's besides the new one being double the size, is the new one is "SLI-Ready". When I was building my computer I opted for the cheaper RAM, but now it was only 10$ more so i figured why not? I get the ram yesterday, swap the sticks, everything works perfectly. Games run much smoother and I couldn't be happier. However, then I thought, why not throw the old sticks in and see if 3 gigs is better than 2? So I put them in, and the system won't boot. I've tried every combination of ram I can think of, single sticks in every slot, just old, just new, etc. The system powers on, all the fans whirr, but i get no visual, and the LED debug screen on my mobo just says "--" rather than the usual numbers. Please don't tell me I fried like everything. . I'm just sitting here on my floor with my case open and I doubt I'll be able to sleep. So I can answer any questions if I haven't provided enough info. Thanks

EDIT: K so after panicking and asking my friend in chat what to do, he reccomends resetting the cmos jumpers. I'm up and booted and off my laptop!