Not the wisest on them either. Try downloading CCleaner (it is free) and run it. It deletes all the unnecessary files including those dreaded ones (index.dat) that can be pulled up by folks you don't want to know every site you have visited.
First check you hard drive capacity and usage. If it is above 80%, you are probably having cache problems. Either delete files and free up space or run disk defrag, or both.
If that doesn't solve the problem, go to the task manager and see what is running resident in memory. Something is hogging your memory. Either delete useless "memory resident" programs, or get more memory.
Finally, any new programs installed may have such a large instruction set they are overrunning your processor. Check your Front Side bus speed. Running several programs at once may be bogging down your I/O throughput.