My computer is about 3-4 years old now. I'm running an Intel Pentium 4 3.2ghz duo, windows XP home, and a Radeon 9800 XT.
So in the middle of some games the graphics on my computer just freeze, (sometimes blackout) and occasionally my speakers will still work but lately instead they start making crazy robot dial-up modem sounding sounds, needless to say alt+f4 ctrl-alt-delete etc don't work I have to hold down the power everytime.
It happens pretty often lately, I've reinstalled my video drivers several times, I wondered though why in my device manager I have a RADEON 9800 XT, then a RADEON 9800 XT - Secondary. I only have one video card, so I don't know what Secondary is. I've also dust busted recently and my computer doesn't typically run that hot so I don't think it'd be an overheating thing.
Now on top of that when I started it like this a second ago when it did it again, nothing happened the screen stayed black. So I turned it off AGAIN and turned it back on and it said "Windows did not start properly" and gave me an option to run windows normally, or last known good configuration. First time I did normally and it didn't work again, then I did good configuration the next time when I got the screen and it came back on.
Plus now my PCI USB card doesn't seem to be working properly either, my wacom and my printer are now showing up as "Unknown USB devices".
EDIT: Well now they miraculously showed up... my computer has gone insane.
EDIT2: Maybe it's the heat... but like I said I've had the computer for almost 4 years and I've never run into this problem before.. though I recently added that PCI USB card under it so maybe its cutting out some of the cards cooling?
Could be your PSU failing, after 4 years I wouldn't be surprised, try to burrow a PSU from a friend, if the issues dissapear then it's the PSU.
Second option is videocard overheating, but I don't think that'll cause your USB to fail, anyway, monitor your cards temp under load (atitools is a good idea) and then try too improve the cooling somehow (removing the addon card maybe or underclocking the 9800)
Hope it helps.
Also, when you come back to update us in the situation post your full specs.
Here's a simple thing to try (it just helped me out)
buy a can of air and open up the case and get to cleaning. Too much dust on system components will cause them to overheat and you think they are failing but in fact they work fine if you maintain them.
Of course, something could be failing but I thought i'd throw this out there. in my 2 cents, its the most obvious cause of an older system acting up