major problems after restarting windows xp service pack 2

my sister has a laptop, same hp notebook type that i use.
she downloaded windows xp service pack 2 and rebooted when told to. however when it reboots the screen now just says "failure to load press a key to continue".

this is the one forum that has always given me great advice and didn't make me feel like a moron, so i figured i'd come here first.
any help you guys could give to solve this probem would be greatly appreciated!