My system is restarting suddenly

[bhaskar_y2s_rit]

My system is restarting suddenly what to do. It is having windows service pack 3. From yesterday it is showing this kind of problem

 

[Combat Wombat]

the best way to fix this is to insert your windows installation disc and boot from disc using "One time Boot menu" it could be called... and then follow the prompts until you have a repair option.. then select repair and let the good times fly...

Then once the good times are over.. complete updates once again... and leave your computer while it updates.