This sounds serious, and after you hear my answer, you might just want to throw your computer out the window.
If your computer CPU overheats, it will freeze the computer.
Some computer vendors who put together their own computers to sell do not do a very good job.
The CPU has something called a "heat sink" to help ventilate the CPU and keep it cool.
Some "heat transfer" goop is supposed to be applied to the CPU before installing the heat sink, and some times an inferior brand of goop is used, so that in time, it loses it's effectiveness.
This may NOT be the cause of your problem, but if it IS, there's only one solution:
Have some one who has computer savvy (a technician or a computer "geek") take your computer apart, clean off the old goop, and apply some new goop, then put your computer back together again.
Once you've done this, you'll need to reinstall Windows, because when the computer stops like this, then you restart it, it bypasses a file which becomes corrupted, and the only cure for this corrupted file is to reinstall Windows.
That's what I need to do to my own PC at home, but I just haven't had time!
A technician (or computer "geek") could check it out to find out if over heating is the problem, but it's sure a lot cheaper than buying a new PC.
Good luck.