Top choice in diagnostics for Win XP, etc?

I have a serious need to try to find shareware or freeware that I can download and would be oriented toward the less technically inclined which would let me do the following:
1] See IF all my RAM is working ok, versus some being dead + how much RAM.
2] Check function, status, and give details on the CPU, Hard Drive, Modem, etc.
3] Determine if my OS is OK, or if there is a corrupted or missing file.

I am trying to find out if I have lost some memory or if there is another issue.

Thanks very much for all advice.

 

Thanks very much for the help.

Do you think if I have the system recovery disk it would be safe to go ahead and format/wipe the hard drive?? All my data is already on another drive.

 

Absolutely!!! If you have all your data backed up, and you have install CD's for all your programs (like Office/Word & Excel, games, etc) then go ahead and format. It's the best way to get your software 100%.