Oblivion frustration

First off, sorry that I've registered and am immediately bringing a problem without contributing myself. But I've actually stopped playing Oblivion entirely because of this, so I feel justified in asking.
Story goes I upgraded my computer quite some time from a socket 754 sempron 64 with 512 megs of RAM to socket AM2 Athlon 64 X2 with a slightly excessive 4 gigs RAM. Essentially there are three reasons I did this - I just like to have the new and good stuff, I wanted Oblivion to run nicer, and I accidentally broke my old motherboard - not sure how.
Anyhow. I kept my old saves, and they're all good, none are corrupted, so I got back to playing my game. My immediate happiness with the beautiful new smooth performance, however, was shortly replaced with horror as I found that after about a minute to maybe four minutes playing, the mouse and keyboard input would stop having any effect at all. Seriously, everything was still working - enemies attacking me etc. - but my mouse does nothing, and my keyboard does nothing - not even the ever-helpful Ctrl+Alt+Del. So, the computer's not crashed, but the only thing that makes a difference to it is the power switch.
Any ideas what's gone wrong? I'm completely at a loss. Completely.

Windows XP and Vista 32 bit versions both have problems running with more than 3 gigs. To fix this you should install the 64bit version of either of these windowses.

Else you'll keep having troubles, and you'd rather use that extra gig instead of laying it next to your pc eh ;)

Be sure to backup your saves. ;)

You're right, of course, about me not getting full use of that last gig. It was a slightly silly decision, seeing as I didn't intend to go to 64 bit, but I thought it just stopped where it could handle up to and ignored the rest... I wouldn't have thought it would have done something like this, particularly only in the one programme. It does say it has only 3.2 gig, which without stretching my mathematical talents I should say matches up to the max in a 32-bit system. But I think I had other reasons to stick with 32-bit. I may have to investigate a dual boot solution.
Thanks for your help, anyhow.
I might try reducing to two gig temporarily to see if that fixes things. Strange I didn't spot that check before, really.

Yeah, it should be normal for windows to ignore it, but it seems it has some problems looking at what your problems are, it seems like a random lockup because it tries to write to memory it can't access ;)

And 64bit vista might be an alot better solution for your processor too, things run alot faster ;)

Right, well. This morning I opened up my caseand removed half my memory and tried out oblivion again. It's been so long, I couldn't remember the cast spell button! Unfortunately, I only had time to kill the frost atronach before it did it again. Looks like quantity wasn't the problem here.

I have to slightly sheepishly admit that I found the answer in the FAQs on the Bethesda site. I'm fairly certain it wasn't there when I last looked...

"Keyboard input problems could be the result of a control peripheral. Editting the Oblivion.ini may correct this issue. The Oblivion.ini file is located in the My Documents\My Games\Oblivion directory. In the [Controls] section, change the "bUse Joystick=1" setting to "bUse Joystick=0" or simply disconnect the peripheral. Make sure the settings are saved. Note, changes to the Oblivion.ini file will not be saved if Oblivion in running when the changes are made."

Strangely, though, I have this problem despite the fact that my computer has not control peripherals saving the mouse and keyboard. That being said, I think Skype decided I had a webcam which I also don't have...

Well, cheers for your help, anyhow, Magus.