Hmmmm,

Given that hardware spec and the specific mention of "services", I would guess Win2000 or XP?

1. Defragment in safe mode is good advice, particularly if you have interactive anti-virus/malware programs running, as that allows the pattern files to be defragmented, so performance is improved.

2. I personally don't like to see a drive with less than 30% free space, performance drops off pretty quickly towards the end [good point Undies~ ]

3. As far as I know the purpose of defragmentation is to improve system performance, and the size of the drive is irrelevant.

4. If the job is restarting you should get a warning message?

Undies~ makes a number of good points for you to consider ( I like the rather enigmatic "I am still just scratching the surface" )

With Win2000/XP and that hardware the job should not take more than 30 minutes in safe mode, based on my experiences.

So:

1. get rid of all obsolete files such as software demos, installation files, AV update files, temporary files etc.
2. Empty browser history and cache files
3. If you have restore points, get rid of those that are too old to be any good.
4. Scan for viruses/adware/spyware
5. Reboot into safe mode, and run the job again.

Good luck

And if you do have an old Windows OS and FAT32 get the free Diskeeper Lite defragmenter.