I guess the easiest way is to run the un-install program but maybe you can't do this if it has been deleted. fortunately there is a manual way of un-registering XLC

Follow these instructions to un-register manually:
1) goto start button and select 'run'
2) type in 'cmd' this will get up a command prompt window.
3) Un-register XLC.dll by typing 'regsvr32/u XLC.dll' into the command prompt window. - you should get a message saying you have succeeded in un-registering.

Hopefully this will work.