Defragmenter keeps starting and stopping

I don't know if this will help you, but it helped me:

I turn off all programs, including the screensaver when defragging. I had some programs that for some reason caused the defragger to restart because they'd write something to the hard disk.

Don't forget to check the "tray" for programs running there. I turn everything off.

General

Anti-Virus apps can interfere with Defrag ... try temporarilly disabling your Norton. Also, consult the documentation for Norton; look for "Protected Recycle Bin". Almost anything running in the background can interfere with Scandisc and Defrag; screesavers, power profiles, auto-updating programs, open chat or messenger applications or email clients, "keep-alive" dial-up connection helpers, calendar reminders, Scheduling Agent ... the list goes on and on. I generally defrag in safemode; you might wanna try that. For your RealPlayer problem, first check Add/Remove programs, and uninstall it there if present. Search for a folder named "Real" or "RealPlayer", most likely in C:\Programs, and delete that folder. Then, equip yourself with Spybot S&D and AdAware[/i][/u]. Following the instructions in the documentation for each, install, update, and configure both for maximum protection, then run run them, one after the other, letting each "fix" whatever it finds.