I have a P4 1.7 Ghz. Gigabyte GA-8SR533P mobo, 256 PC 2100 DDR, Geforce FX 5200 AGP 128 Mb video, onboard sound, and a linksys wmp11 wireless network adapter. and 20Gb HD. I just bought this computer cheaply for a friend's christmas gift. Installed Win XP, then installed drivers for all components. I have a cable connection, so when I'm online, everything is working fine. But, when I go to download files, windows will either freeze, or just restart. This has been especially happening when I try to download/install SP2, but there are other times when i'm not downloading that the computer will just shut off and restart. I've run AVG anti virus, Macafee stinger, and ms antispyware, and none of them found anything. Also, I've swapped out power supplies, RAM, and HD, but it didn't help. I was thinking the network card may be the problem, but i tested that with another one as well. So I'm thinking its either the mobo or cpu, but I need to know if anyone else has any other ideas that I haven't thought of yet. I really need to get this thing going. Thanks.
Check to see if the network card is in a slot that is sharing the same interrupt at the onboard sound. If so, move it to another slot that uses a different interrupt from your other devices. Also, try to find a slot that doesn't use bus mastering.
I would also try to run the system in safe mode with and without networking. Try the same things and see if you have the same problem. If you do, then you can rule out startup software.
I would personally format the hard drive, remove any components that are not necessary for the machine to operate (i.e. sound card, network card etc), then re-install XP on barebones hardware. Following this, install one component at a time, ie. install the network card then reboot and install drivers, shut system down, install sound card, re-boot and install drivers for it. This usually helps windows assign hardware components interrupts etc, in a progressive order rather than all at once. I had similar problems when XP first came out, and this method seemed to work.
If this doesn't work, ditch the P4 crap and buy an Athlon + AMD motherboard.