computer locks during record or playback

When it feels like it the computer locks up during record and or playback. I can continue only after hitting Ctrl,alt,del. When the tack window opens I hit cancel and return to the cubase screen and then the transport bar will let me stop the recording or playback. This happens without regard to the specifiic cubase file and totally random. Jeff Deno at Steinberg support has yet to resolve this problem for me. I believe it to be a program issue and so does my computer builder.

Which: Cubase version, 64/32 bit, Operating System, Audio interface etc etc?