Sorry, but the clue isn't in the details of your post. It could have been as simple as XP doing some USB Power Saving and you haven't turned that off yet. But that's just one of hundred guesses. Sorry I can't see it from here yet.
I apologize in advance for bugging you guys with such a minor annoyance. I used Norton AV for yrs before replacing it with free AVG Anti-Virus/Spyware. Everything worked fine until at some point I noticed a problem. Whenever I left my XP alone for a few hours, when I returned and tried to open any document on my Desktop, the processor would make a Search-like noise for 35 seconds before it would come back with my options to Open the file, etc. From that moment on I could open any Desktop file immediately, as usual. I have no idea if this glitch is related to my recent AVG software or not. (I submitted this problem to the Free AVG Forum last night, but their Moderator got his knickers in a twist and blamed XP.) Has anyone else noticed a similar problem with their XP system, with or without AVG software? I haven't tried anything to repair the problem. I use Win XP HE ver. 5.1, SP2, on a desktop system.