Help on Suspend and Hybernate

I recently had to re-install Windows XP Prof. SP2 to correct a problem. Everything went fine, except that now my machine won?t hibernate or suspend (which it did before). Am I missing a file? How can I find out? What can I do? I have been thinking of re-installing WXP again but I?m not sure I should – don?t wanna screw up something else. It sounds like I don?t know much about WXP, but I do know some, I?m just a little insecure. Could any one help me out?