A friend asked me to look at his computer, an LG running Windows 7. It had slowed to a crawl and any applications opened as disjointed blocks of the final window, which would eventually appear. I help him maintain his unit and am there periodically to defrag and run ccleaner, for example, and generally make sure he doesn't have too much stuff running at startup. He has 2 GB RAM of which usually ~700 MB is being used for overhead. I tried restarting and then none of his apps would run. Unfortunately, I'm home now so can't give the exact error messages, but, e.g., when I tried Chrome I got a message, something to the effect that the computer couldn't locate a valid image (I'm a Mac user and I assume that means something akin to disk image?). MS Word gave a different message, but again, something to the effect that it couldn't locate the program.
Any ideas, based on the rather vague information I've provided?