A couple of things:
Try not to double post, especially if it's just telling others to hurry up and find info for you. People who may be able to help could be, due to time differences, asleep or at work. You won't get an answer immediately, so try leaving it more than 47 minutes.
This is not exactly a SP issue, so might be better in the Community forum or something like that. It'd get different exposure too. I am so glad you used OT though.
This issue is an issue with your computer and its files, so we aren't likely to know a huge amount about individual files and why they're corrupt/missing. Just wondering, why do we have to do all the searching for you? I googled psapi.dll and found instantly 9+ pages (without reading much) on how to and where to download/install this file, as well as info on what it does.
Don't expect me to do this again, but I am curious to what it is, so here's a quote I found within 1 minute of searching.
Description:
psapi.dll is a library file which provides support for process status.
Not that helpful, but that's what it does.
Anyway, did you try google? It has a vast knowledge, and many helpful sites.
Sorry if this seems as if I'm a little irritated, but the first thing that should be done with a computer issue is google, especially when it's specific and has a huge amount of info on it. Find out what you can, and if that doesn't help, ask for assistance.
If none of this (including google) doesn't help you whatsoever, I'll be happy to have a deeper look to try to help you out.