SiSoftware's Sandra (System ANalyser, Diagnostic and Reporting assistant) is a popular troubleshooting tool.

It won't actually fix your PC for you, but it can analyse the various components within your PC and help you figure out where your problems lie.

It can also run a number of benchmark tests to see if your PC is performing properly. This is the free, basic version of the program, but there are three other versions to choose from - Pro Home, Pro Business, Engineer.

Note that this is for personal home-use only and now supports Windows Vista, so you can benchmark and test your new Vista PC.