Sounds like it is busy doing work in the background when that happens. You may have a cluttered system. Try running CCleaner and see if it helps. Do the Clean and Registry both. You may have to run it more than once if the system is extremely full of crap. http://www.piriform.com/ccleaner/download
Then check your System Configuration/Start Up to see how many pgms are starting and if there are any you can eliminate.