Serious Computer Problem

Today, my computer started freaking out. The mouse wouldn't stop right-clicking like crazy, so I decided to run a malware scan while off of the internet (disconnected). At first, everything was okay. Malwarebytes needed to update, so I let it. Restarted the computer, which seemed to fix my problems. Started a scan. Briefly connected back onto the Internet to look for a phone number, then disconnected again. Mouse started going batshit again, moreso than before, and then SHOOMP. My computer turned itself right off. Tried turning it back on and it started to, then stopped. whaaaaat is happening i am really scared

This is probably something you won't fix. PSU (power supply) is always the first place to start looking... and by "looking" I mean finding another one to test. More likely culprit is motherboard.

OH MY GOD FINALLY the 3ds does not handle this forum well. Tried turning it back on in safe mode and got to the desktop before it shut itself off again. see, this happened with my last computer, the whole 'shut itself off' thing. At this point, I'm just not gonna touch it until someone that knows computers can come look at it. also why does even the mobile version of the forum cause 3ds hiccups?

OH MY GOD FINALLY the 3ds does not handle this forum well. Tried turning it back on in safe mode and got to the desktop before it shut itself off again. see, this happened with my last computer, the whole 'shut itself off' thing. At this point, I'm just not gonna touch it until someone that knows computers can come look at it. also why does even the mobile version of the forum cause 3ds hiccups?

Try this first.

Turn the PC off and unplug all the cables from the back - power, monitor, printers, keyboard, mouse, the lot.
Then hold the power button in for about a minute before connecting it all back up again and restarting it up.

If that doesn't work, try plugging your mouse into a different USB slot (if you have a ps/2 mouse, try a USB mouse instead).

If that doesn't work, you may be able to solve it by reinstalling motherboard and controller drivers.

If that doesn't work then it's likely that you have some issue with the motherboard (which might be caused by a faulty PSU as Pogo says).

I love how it seems to make you post everything twice.

Your suffering is my amusement >:D

Also I dunno how to fix

That first bit helped it run, but I'm still wondering what was making that go on in the first place.
Either way, you are my hero times ten million and I love you.

EDIT: Problem has been narrowed down to the mouse. When I use the cursor with my tablet, everything is fine. If I use my mouse, within moments, it starts doing crazy right-clicking.

this is ridiculous.

It's possible you have a sticky microswitch or a shorted circuit in the mouse itself. If you use a different mouse is it ok?

YOU ARE ALL FUCKING BIG MOUSE

Now that's some cred right there. You get a like.