My computer shuts down without any warnings.

Hello,

so I had this computer already for two years now and lately and often it started to restart and shut down on it own.

First I thought it to be an virus. Did a clean format and reinstall Windows, but still the same thing. The funny thing it always restarts when someone is using the computer, like browsing on the internet or watching a video and I am not talking about games here, just your typical usage of computer result in it shutting down.

Theirs two types of shutting down:
1. While watching a movie the monitor shuts down, the sounds is still playing and the fan in the computer starts to run like crazy. In this case I always have to shut it down on my own.
2. While browsing on the web and I mean opening several of windows the computer just restarts itself without any warning.

I think the problem could be in my BIOS or in my power supply.

In Even Viewer I get this:

- Provider

[ Name] Microsoft-Windows-Kernel-Power
[ Guid] {331C3B3A-2005-44C2-AC5E-77220C37D6B4}

EventID 41

Version 2

Level 1

Task 63

Opcode 0

Keywords 0x8000000000000002

- TimeCreated

[ SystemTime] 2013-03-18T12:55:11.537210600Z

EventRecordID 2430

&

- Provider

[ Name] Microsoft-Windows-Eventlog
[ Guid] {fc65ddd8-d6ef-4962-83d5-6e5cfe9ce148}

EventID 1101

Version 0

Level 2

Task 101

Opcode 0

Keywords 0x4020000000000000

- TimeCreated

[ SystemTime] 2013-03-18T12:55:20.304426000Z

EventRecordID 828

Correlation

- Execution

[ ProcessID] 856
[ ThreadID] 1052