Browse to the Windows directory via command prompt. To do this:

1) Click start
2) Click run
3) Type cmd
4) Type cd c:\windows
5) Press enter

Type 

lodctr /r:PerfStringBackup.INI and press enter

If the above does not help, follow the instructions below:

1) Search for perf*.dat in the C:\I386 folder (If the I386 folder does not exist, see operating system CD)
2) Copy all perf*.dat files to the C:\Windows\system32 folder
3) Launch perfmon again