This might help:-
http://www.fixya.com/support/t122832-powerdown_after_few_seconds
I actually found your request because I am in the same situation for the 2nd time! I'v had the machine for about 6 years now and the last time it went down was 3 years ago.
Its a component known as STRG6353 and can be purchased from http://www.dalbani.co.uk/catalogue/product_details.php?id=28531
Its fairly easy to change if you know how to use a soldering iron.
IB
December 2009