task manager can stop working

Task manager can stop working for a number of reasons, I'll go over some fixes from easiest to hardest

See if taskmgr exists
1) Click Start -> Search
2) Click All files and folders
3) Search for taskmgr and set location to %systemroot% (usually C:\Windows or C:\winnt). You can actually type "%systemroot%" as well.
4) You should find in the list:
%systemroot%\system32\taskmgr.exe 133KB

If you cannot find this file, you can extract it off your XP CD again. Refer to APPENDIX on how to extract the file. The help files CHM and HLP are not needed to run taskmgr.
Once the files are in place, try running taskmgr again. Try double-clicking on the program icon itself in the system32 folder.