I need help with...

Hi
so i have this problem, my computer turns on and seems like everything is working, the harddrive sounds like windows is working in the background
but nothing comes on the monitor. I tried another graphics card, (thinking that was the problem) and that partially helped, then that stopped working (the fans on both of them still work) now im starting to think that it is the psu
or mobo. Can someone let me know what they think it is.

Here are my specs:
Gigabyte GA-K8N-SLI Socket 939 NVIDIA nForce4 SLI ATX AMD Motherboard
ASPIRE ATX-AS520W BLACK ATX 520W Power Supply
AMD Athlon 64 3200+ Venice 1GHz FSB Socket 939 Processor
Maxtor DiamondMax 10 6L200M0 200GB 7200 RPM Serial ATA150 Hard Drive
PNY VCG6600GXPB Geforce 6600GT 128MB GDDR3 PCI Express x16 Video Card
CORSAIR ValueSelect 1GB (2 x 512MB) DDR SDRAM DDR 400 (PC 3200)
with a dvd burner and floppy

this started after i played guild wars, a bluescreen came on (not bsod though) and after i restarted the bios screen started blotching and after the windows boot screen the moniter went into powersave mode...
i tried another monitor and that didnt help... anyhelp?
asap before my dad find out ( )