The problem may be caused by startup program(s), hardware (HW), driver, or Windows.
Need to narrow it down.
Try the following steps. This will help you to troubleshoot. If you are willing, you will find the answer. If freezing continues, go to the next step.
1. Disable all startup programs.
If the freezing disappears, one or more startup programs are the cause.
Able (and disable) half the programs at a time to find the bad ones.
2. Update the video driver.
3. Remove all non-essential HW (all PCI cards, FD, Zip, CD-ROMs, 2nd HD, and so on).
3. Do a hard drive (HD) diagnostic test.
Your HD might have some bad sectors.
If there are bad sectors, backup data and replace the HD.
4. Clean install Windows in a spare or new HD.
5. Replace Power supply, RAM, video card, CPU, and motherboard one at a time.
If you do not have known good replacements, take your system to a computer store.