By any chance, have you overclocked your system? If so, try lowering down the FSB speed. Also, look on your motherboard for bent capacitors, (they look like batteries in plastic) burn marks, and cracks. That could be the problem, also.
Do you have an antivirus? If not, go to www.grisoft.com and download the free version of AVG antivirus, update the data file, and scan for viruses.
Go to Start>All Programs>Accessories>System Tools>System Restore. Do you remember the date or around it when this wasn't happening? Click on or before that data when you know it was working, and let it restore to that point. I would back up your data, first.
If none of this works, you may need to run System Recovery, or a fresh or repair install of Windows.
Do you have an antivirus? If not, go to www.grisoft.com and download the free version of AVG antivirus, update the data file, and scan for viruses.
Go to Start>All Programs>Accessories>System Tools>System Restore. Do you remember the date or around it when this wasn't happening? Click on or before that data when you know it was working, and let it restore to that point. I would back up your data, first.
If none of this works, you may need to run System Recovery, or a fresh or repair install of Windows.