Every few days or weeks, Windows just freaks out. Sometimes it comes up with an error "Windows has just recovered from a serious error", the screen being in 16 colour etc, keyboard and mouse not working. I reboot like it tells me to, and then windows claims one of the directories (\system32\something) is missing. I can't get into windows. Other time, I listen to an MP3 or something, anything memory intensive such as sound editing/recording, and the system freezes, the sound getting stuck. Yesterday, the MP3 went all crackly, the monitor lost signal and I couldn't use the PC. I restarted it, and it complained while in windows that system files were being overwritten with unrecognized versions and I should insert the OS disc. So I did. Then I restarted, and then I couldn't login because of license errors or something. I rebooted again, and then the PC rebooted itself whenever it got to the login screen. This happens quite alot. I've been told it could be my RAM chips are dodgy, but I ran Memtest for roughly 45 mins/1hr and no errors were found. What could it be?