100% CPU on explorer.exe

This happened just a few days ago. I've been trying to transfer some files from my Flash drive to my PC but after a while my Windows Explorer freezes and I hear a loud buzzing sound on my PC. I opened up Task Manager and saw explorer.exe eating up most of the CPU processing and boosting it to 100%. Shutting down explorer.exe reduced the processing back to less than 10%, but it returns again when I tried to transfer the files. I noticed though that I do not see the CPU go up if I browse within the PC (at most it goes to 50%), but it does go up whenever I access the Flash Drive. Take note that my PC is not connected to the internet, so I find it doubtful it got a virus (it's been offline for quite a long time). It is however quite old at 7 years running on XP SP2, 1.5 Gigs of RAM, and either a Pentium 3/4 Processer at less than 400 Ghz.

"Not connected to the internet" is certainly no indicator if the computer is infected or not. Plugging an infected flash drive into it is all that is needed. At your maintenance level, your computer would get infected by breathing too close to it. There could be any number of hardware issues inside the system. The buzzing noise is strange and could be an indicator, but without knowing what that noise is its hard to tell. It could just be fan kicking on higher because of the high CPU load. If you have lots of files on the flash drives (thousands) it can take a very long time for explorer to process them - you just have to wait. Sometimes, if they are video files or other types of media files, you may have some kind of program or codec on your computer that is trying to process the content of those files and it is not functioning normally. Anti-virus software could also be causing some kind of issue on the machine as it tries to process each one of those files. Hard drive lights, and/or flash drive lights should be an indicator if anything is happening at all. Maybe you just haven't waited long enough. I guess the best suggestion I could give at this point is to try to start the system in a limited startup mode for now. Click start -> run -> type 'msconfig' and press ENTER. Choose the services tab, check "hide all microsoft services" and click 'disable all.' Apply your settings. Click the Startup tab, click disable all, and apply your settings. Click OK and you will be asked to reboot. Go ahead and reboot and try your transfer again. If it works now, this indicates it is one of the many programs you have running on your computer under normal mode. When you are done, you can switch back to normal mode. Run msconfig again, under the general tab, select normal mode, apply your changes and restart again - or, you can use msconfig to enable/disable groups of items until you narrow it down to the program causing you a problem. Good luck.

It may likely be the Flash Drive itself. I decided to reboot the system but with the Flash Drive removed and I didn't see any problems (though the CPU at times goes up to 50%, but no higher than that). When I re-plugged my USB Drive back in, the 100% CPU spike stopped.