very long delay on booting windows

[ntsaoussis]

When starting up my Imac in Windows, it takes more than half an hour to boot. After 5-10 minutes, I hear the windows sound and then the grey screen. This repeats 5-10 times before windows boots up (windows xp sp2).
This happened suddenly after about 3 months of normal operation i.e. both mac os and windows started up quickly.
I also have a mac book pro which boots both operating systems very quickly.
Any ideas/thoughts?
Any help would be much aprreciated

cheers