You can probably get away with not reformatting as long as there isn't too much junk trashing your resources.
I'm not sure what good a registry cleaner will do though. Were you able to run the defrag, or wouldn't it let you?
The defrag won't run unless there's at least 10% (i think) free space on the drive being defragmented. Otherwise, you might just have to delete and uninstall some crap you don't use anymore.
Also, let the defrag run overnight. When it's really defragmented, it can take hours.
If you're a battery, you're either working or you're dead....