Last week, I was unable to create a new folder on a previously reliable machine running Windows XP 64 bit. Got an error "Media is protected" for entire hard drive partition. Attributes of partition showed partition was NOT "Read only"

Tried DISKPART ATT VOL CLEAR READONLY as elsewhere suggested, no help.

Soon thereafter, entire hard drive (all 3 partitions, C:\, D:\, E:\) showed as returned "Media is protected" errors. Figuring the RAID controller was bad, moved critical data files under Safe Mode w/networking to new different machine running WIN7 Ultimate 64 bit.

Now getting errors on Win7 machine -- All the copied over Thunderbird files are Read-only, previously accessible Excel spreadsheets are unmodifiable as marked "read Only". and Acrobat wants to re-register because "Configuration has changed". None of the files, drives, or volumes in question show the "read only" attribute set in Properties.

Same problem is happening on at least two different Win7 64 bit machines. Comodo, Malwarebytes, Spybot and MS MRT come up clean. MS Sysinternals Rootkit Revealer won't run -- crashes with error. Process Explorer shows nothing strange.
I've installed all recommended MS updates except IE9, ('cause I have to keep IE8 for specific apps). 'Net searches show similar problems in 2009 but none of the suggested fixes have help.

Rolled systems back to earliest restore points, but problems seem to be cropping up again. Lost 6 years of eMaiil.
Any suggestions on a fix or an approach to a fix -- ?new virus -- ?incompatible MS update -- I really need to get the office systems up and running again. Is there some other error that is mis-reported as a Media Protection error?