Well, you haven't given us any details about your computer. What make and model? Hardware specs? Did the problem start all of a sudden or has it been getting gradually worse? Did you make any changes to your system before this started?
Explain the behavior in more detail. Does this happen right after you turn the computer on or after it's been on for awhile? How long after it's been on? Does it seem to vary, depending on how heavy you're tasking your computer?
What are your normal maintenance procedures (disk cleanup, defrag, spyware removal)? What other protections (virus, firewall) do you use?
