referenced memory error!

I keep gettting this referenced memory error whenever i log off windows xp on my computer. I don't have the time to write it all down, but it's says something like, "The instrustion 0xf0d0f5a" referenced memory could not be read, press ok to terminate" it says it every single time and there are various messages. My computer has been running very slowly, i have tried every virus scanner out there - thinking it was a virus, but to no avail, not to mention my keyboard keeps unistalling itself randomly and my mouse just stops working every few minutes. I have had several crashes recently, where i have had to go back to my last back up date.

I use xp home and use zone alarm as my firewall (if that helps)

Please help, i am going nearly insane here

Thanks