Is it a laptop or desktop??? Both need lots of air circulation. First, you need to make sure your laptop or desktop:
1. is placed on a hard, flat surface for use
2. has 360 degrees of air circulation
3. is used in a fairly comfortable room temperature
4. has no dust or debris in or around any of the air circulation grills
4. fans are free of dust and debris and that they run smoothly and quietly
5. You may need to buy a laptop cooler base for under your laptop
6. Make sure the inside of the case is free of dust and debris (If you aren’t competent to work inside the box safely and correctly, then seek professional help).
7. Check each fan individually by sight and sound to make sure each one is running free, quietly, and completely free of dust buildup on the blades. This includes intake fans, CPU fan, video card fan, exhaust fan, power supply fan, & any others you might have. (If you aren’t competent to work inside the box safely and correctly, then seek professional help).
8. Unseat your RAM sticks and vacuum the slots. Reseat the sticks securely. Do the same for any other cards inside. (If you aren’t competent to work inside the box safely and correctly, then seek professional help).
Then, I'd:
Uninstall all those free web browser add-ons
Uninstall all the extraneous programs you got for free like Limewire & such
Delete all your temporary internet files & cookies
Edit your startup files and delete what you don't need
Run disk cleanup
Download Avira Anti-virus
Download Spybot Search & Destroy
Download Ad-Aware SE personal
Download ZoneAlarm personal edition free firewall
Download Ccleaner
Reboot and uninstall all your anit-virus stuff, all your spyware stuff, and all your malware stuff. De-activate your Windows Firewall
Deactivate your system restore
Reboot and install ZoneAlarm, then install Avira, Spybot, Ccleaner, and Ad-Aware. Update these programs one at a time.
Reboot into safe mode and run a full scan using Avira, Spybot, Ccleaner, and Ad-Aware.
Reboot & Reactivate system restore & create a restore point
Run disk defrag.
Reboot & Create a restore point
Start>right-click on My Computer>Properties>Advanced>Performance Settings>Advanced>Virtual Memory Change>Click Custom & enter 1.5 times your system memory size. For ex, if you have 1Gb RAM, enter 1500 in both blocks, then click Set. OK to close that box, then in the Advanced folder make sure you select "Programs" in both sections.
Reboot & Create a restore point
Update Windows & IE to the latest version and/or patch. Search the Microsoft Knowledge Base for known IE problems.
Get into your Device Manager and update your video driver first to make sure you have the latest version. Run for several days to see if your problem is solved. If not, continue to update your hardware drivers until your computer no longer locks up.
Good Luck