That message from the Event Viewer could certainly be related to this
problem, but I'm afraid I'm not sure how to go about fixing it. Is the error
continuing to occur, or did it just occur once?
I'd say that, if it was a one-time error, and if it occurred just before the
loss of Disk Management functionality, you might try reverting to the restore
point closest in proximity but dated BEFORE the error occurred. If you use a
restore point you will have to re-apply any software / OS updates that had
been applied to the system since the time that restore point was created.
If the error is ongoing that indicates a serious misconfiguration of the OS.
It might be fixed by a repair installation of the OS. That fix would, of
course, entail reapplying all Microsoft updates since the system was new,
though most updates applied to most non-MS software might not be affected
adversely.
I have to wonder why the error condition occurred in the first place. Did
you look at my other questions concerning whether there was anything unusual
about the configuration of the system? For example, did you have to load disk
drivers not included in the OS database, or would this have been an upgrade
installation of Vista on top of an earlier OS, etc.?