Defrag will not run?

I want to install a new program on my laptop running Xp service pack 3 the instructions tell me to do a full defrag before I install the program, but the system will not allow me to run the defrag, it keeps comming up with a message " chkdsk is scheduled to run? run chkdsk/f" I have had a look in the "scheduled folder" and it shows no sheduled tasks?