PC completly freezes for no apperant reason

Scaleo

Honorable
Mar 7, 2012
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10,680
Hello everyone,

Recently I have been expierencing some very odd behaviour from my pc.
Usually I use the pc everyday and it works just fine and all, but today I only used at the end of the day and tried to open up my Gmail after the pc completly stopped responding, by that I mean that the background completly freezes but I can still move the cursor around, but it won't respond to my given commands, like trying to go to start to reboot the pc.
So I had to turn of the powerswitch, turned it back on, and the monitor displayed a blackscreen saying something like ''insert installation disk, or reboot pc'', but I am not exactly sure what it is said though.
I rebooted it via powerswitch again, the pc worked fine only I noticed it acting weird in the sense that it sometimes freezed when playing BF4, this never happened before as the game runned very smoothly before, and YouTube video's tend to not play automaticly after I click on one, rather that I have to manually but the timebar on 0 and press ''play'' in order to make the video run, and even the video has lag, the audio is playing in the background but the images are just frozen till I manually choose another timeline of the video.
So the pc completly froze a second time, with the audio still playing in the background but the the desktop not responding, I tried to open start but it crashed (I use Windows 8.1)

TL:DR, computer completly freezes and stops responding when performing simple tasks.
(PS: pc is relativly new, and the possibility of downloaded viruses are non existent)
 
Solution
If your system remains stable after your updated antivirus has removed the Trojan then it was possibly the Trojan that was causing your system to freeze.

Scaleo

Honorable
Mar 7, 2012
239
0
10,680
CPU: Core I7 3770 3.40GHz
RAM: 8GB
GPU: GTX660
Had to write in a hurry cause pc could freeze up any second again.
Ran myself a memory test provided by Windows itself, no errors found.
Updated my Antivirus (from AVG 2013 to AVG 2014 with license).
Turned out I had a Trojan horse and I have no idea how since I did not download anything but games from Steam and Origin.
Pc seems stable so far.
 

Scaleo

Honorable
Mar 7, 2012
239
0
10,680

That's a huge relief than, but how can I avoid letting this happen again? Apart from keeping my AVG up to date.
I ask this cause I have no idea at all how I got a Trojan virus, I only use Steam, Origin, YouTube, and some forums like Tomshardware and Wiki's.