sp3 has caused a fault

sp3 has caused a fault with my fathers pc. since instalation he cannot
access his pc, it asks for him to activate it again. is there anything i can
do to get it back up and running for him. i could do a reinstall but he has
programs on his system that he cannot replace that easy as he no longer has
the install disks for them or has lost the product key for them. please help
as he has to do his tax returns by the end of the month and is starting to
get very worried as pensioners do. thank you for any help you can give.
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cheers now SCOTT_Q