Problem accessing CD/DVD and external devices

My setup with Windows XP, two external hard drives connected via USB, IPOD

USB and CD/DVD was all working fine.

Same problem with a USB memory stick.

Now I can't access any of the above - they all show under windows explorer

with a drive letter, but when I try and access them I get G:\is not

accessible, Access is Denied.

If I start in safe mode all works fine. If I map the external hard drives as

a network drive I can access them.

Any ideas what has gone wrong? The PC is used by the family, I can't see any

recent suspect software, virus software is all current.