Can't Shutdown or Defrag

1. When i try to shutdown, i get the normal, saving settings message,
shutting down system message, then i get a blank desktop with a frozen mouse
pointer.....it just freezes here at this point....then i have to manually
power down........why can't it shut down properly.....it used to before.


2. When i try to defrag my c drive i get the message:

Volume (c has 74% free space, but only 0% is available for use by disk
defragmenter. To run effectively, disk defragmenter requires at least 15%
usable free space. Before running, you should delete some or move some files
to increase usable free space......

I've down a chkdsk, & error-checking on drive c, it didn't find any errors.
I have tons of free gigs, why doesn't defrag recognize the free space????

please help
w