Computer randomly restarts itself.. WHY?!?

It's happened twice while i've been running quite a few things at once the other night, when scanning for viruses and cleaning up space

I had these programs on:

Avast(scanning)

Windows Defender(Scanning)

Disk cleanup

Defrag

Ccleaner

Lavasoft AD Aware SE personal

Spyboy - Search and destroy

Spyware doctor

So that's like EIGHT programs on at once

Is this why my computer restarted itself?

Computer randomly restarts itself.. WHY?!?computers

Sounds like an overheating issue.

You have some software that don't play nice together. All that adaware and spyware programs need to go away except for one. Choose your favorite to keep and get rid of the rest.

Ccleaner, Defender, (Disk cleanup - Windows) can stay, then choose one from the remaining to keep.

Computer randomly restarts itself.. WHY?!?hijack this

It was probably Windows Automatic Updates - turn them off in Control Panel
This could be a hardware problem. Try downloading memtest to check your RAM. Just burn it to CD and boot off of it and it will run the test for you. Also, does it power off after a certain interval, like every 30 minutes? If so, it could be overheating. Check all of your fans and make sure they're working okay. You can also download a program like Speedfan to monitor internal temps in your PC.
virus...................
It's probably corupted mate you may need to re-install windows.
I had this problem with XP a few years ago on this computer, when XP first came out. The First XP I had was version 5.