your computer needs to shut down, your computer needs to shut down - help please!

Sounds like a kernel panic. These are generally hardware related, often due to faulty or poorly seated RAM modules.

What is a Kernel Panic?

http://support.apple.com/kb/TS3742

and http://support.apple.com/kb/TS1892?viewlocale=en_US

http://developer.apple.com/mac/library/technotes/tn2002/tn2063.html

More details here:

http://www.thexlab.com/faqs/kernelpanics.html

Useful articles on how to avoid and eliminate kernel panics here:

http://reviews.cnet.com/8301-13727_7-10344626-263.html?tag=mfiredir

http://www.macworld.com/article/2027201/how-to-troubleshoot-a-kernel-panic.html# tk.nl_mwhelp

Please post the complete text of the panic report, not a screenshot.