Windows 7 Ultimate 64 bit crash

[BigFinish]

Guys, I'm using Windows 7 Ultimate Edition x64 on my PC. Occasionally my system crashes without any warning. The event viewer referred to the event as :-
Kernel-Power
Event id - 41
Task Category - 63
It's random, some days it won't crash at all, on others, like today, it kept crashing again and again.
At first it was a crash in the middle of the session. After that I restart the system, the log-in screen comes, I enter my password and when I hit enter, before logging in it crashes. Now, I took my 8400 GS off the motherboard and turned the sytem on with the integrated GeForce 7100 mGPU. It started normally.
It seems it crashes for no reason at all, I have all the latest drivers, my power supply is adequate (450 W). Please help me out here.

 

[Tews]

Are you getting a BSOD? If so attach the .dmp file for anaylsis...

[1 - Novice] How to ask for help with a BSOD problem

 

[BigFinish]

No, I'm not getting a BSOD. It's just a complete shut down.

 

[Tews]

Enter viewer in the search box and open up the event viewer...Windows log...applications and check for any critical errors (red circle) and take a screenshot, then attach it to your next post so we can take a look at it...

 

[BigFinish]

There isn't any error in the applications section. But the administrative section has got plenty of them.
Shall I upload those errors, or is it unnecessary?

 

[BigFinish]

GUys I need help..pleaase...it's hard to deal with a randomly booting PC !! Can't work or do anything. I asked if it would be fruitful to post the screenshot of the admininstrative events, no reply on that. I'm posting both of them now.

Log Name: System
Source: Microsoft-Windows-Kernel-Power
Date: 17-02-2010 11:59:26
Event ID: 41
Task Category: (63)
Level: Critical
Keywords: (2)
User: SYSTEM
Computer: Batcomputer
Description:
The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
<System>
<Provider Name="Microsoft-Windows-Kernel-Power" Guid="{331C3B3A-2005-44C2-AC5E-77220C37D6B4}" />
<EventID>41</EventID>
<Version>2</Version>
<Level>1</Level>
<Task>63</Task>
<Opcode>0</Opcode>
<Keywords>0x8000000000000002</Keywords>
<TimeCreated SystemTime="2010-02-17T06:29:26.578125000Z" />
<EventRecordID>1281</EventRecordID>
<Correlation />
<Execution ProcessID="4" ThreadID="8" />
<Channel>System</Channel>
<Computer>Batcomputer</Computer>
<Security UserID="S-1-5-18" />
</System>
<EventData>
<Data Name="BugcheckCode">0</Data>
<Data Name="BugcheckParameter1">0x0</Data>
<Data Name="BugcheckParameter2">0x0</Data>
<Data Name="BugcheckParameter3">0x0</Data>
<Data Name="BugcheckParameter4">0x0</Data>
<Data Name="SleepInProgress">false</Data>
<Data Name="PowerButtonTimestamp">0</Data>
</EventData>
</Event>