dead computer advice

Hi everyone. My computer died. It just froze up while my son was playing a game (not even an up to date game). After I turned off the power supply and rebooted, all the lights and fans come on, but nothing was displayed on the monitor. After the third or fourth reboot attempt, it did start it's normal boot sequence, but hung up. I happened to still have my old video card, so I put it in and it worked fine for about a half hour and then the same thing happened again. I'm thinking the power supply is OK, and now the video card as well. Since this happened in the winter (and with no new software demands on the system, I am thinking the CPU may be OK as well.
Unfortunately, I don't have a pile of computer parts lying around that will enable me to test and eliminate the motherboard so I am going out on a limb and assuming this is the problem. Is this a good assumption? Would I be better off bringing to a computer build store and pay them to tell me what is F'd up? If I change the mobo, I would like to upgrade to AM3, but does this mean I have to trash my RAM too? What step would you take if you were in my situation? I don't mind spending money, but I want the money spent to fix the problem rather than start a string of trial and error.


BTW, here are my computer specs...

GIGABYTE GA-MA770-DS3 AM2+/AM2 AMD 770 ATX All Solid Capacitor AMD Motherboard
AMD Athlon 64 X2 4800+ Brisbane 2.5GHz 2 x 512KB L2 Cache Socket AM2 65W Dual-Core Processor
PNY VCGGTX260CXPB GeForce GTX 260 Core 216 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card
Maxtor Ultra 16 300GB SATA hard drive
CORSAIR Dominator 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory
LG Black 22X (CAV) DVD+R 8X DVD+RW 16X DVD+R DL 22X (CAV) DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 22X DVD±R DVD Burner
CORSAIR CMPSU-520HX 520W ATX EPS12V PS/2 MODULAR POWER SUPPLY
MNTR ACER|LCD 22" 5MS X223WBD R
Antec Nine Hundred Black Steel ATX Mid Tower Computer Case
Windows XP home version

 

That's a good machine! Have you monitored temperatures, checked for loose connections, ran Maxtor's drive utility, checked your RAM using memtest 86+... Just a few things to check and eliminate first. Another thing is your PSU, even though it's a good make and all, you are right on the edge of what the GTX260 needs. I'm not saying that's it but it often is.

 

Yup, PSU.

Had this problem on several boxes when the boss decided to upgrade his janky old workstations. Even though they were rated, they were all 5-6 years old and had become marginal at best.