It goes on for a few seconds, is then released and is back to normal until it does it again. Similarly, the cursor freezes and won't budge, even if you move the mouse all over. The programs inside your computer are fighting over some scare commodity. Clearly, this is not the way things are supposed to work. The most likely culprit is a lack of memory, specifically virtual memory .
Virtual memory is a trick used to expand the total amount of memory available.
Your computer only has so many megabytes of RAM memory in physical chips. The operating system increases this number by using a portion of the hard drive to supplement memory. The computer juggles data between the RAM chips and the hard drive as needed. The operating system keeps the important stuff in physical memory, and stores the less important stuff in virtual memory. Well, okay, that's how virtual memory is supposed to operate in theory.