Installers freeze when creating system restore point



I have an Acer Aspire 5920 laptop running Vista Home Premium and I'm having
problems installing any new software (even things as simple as WinZip); the
installations always freeze near the end and never complete. I posted this
question in another forum, and someone suggested a problem with System
Restore, since the installers generally try to create a restore point. I
turned on logging and sure enough, I see this as the last line in the log:

MSI (s) (4C:18) [21:56:53:241]: Calling SRSetRestorePoint API.
dwRestorePtType: 0, dwEventType: 102, llSequenceNumber: 0, szDescription:
"Installed iTunes".

and nothing more. I've let it run overnight, but it never completes.

I took a look at the properties for "System Protection" in Control Panel,
and sure enough, it appears to be hosed. The "System Restore..." and
"Create..." buttons are greyed out, and under Available Disks, it just says
"Searching...". If I let it run for at least an hour, eventually it finishes
searching, but then claims that for the C: drive, there are no restore points.

Worse, after the searching completes, and the various buttons on the dialog
ungrey themselves, I tried hitting the "System Restore..." button, hoping to
see some additional options, but nothing happens when I do that. Do it again,
and I
get "The System Restore Wizard is already running. The program will now exit."

It seems that somehow, I need to reset, reconfigure, or (horrors!) reinstall
at least the System Restore portion of the OS, or worse, the entire OS. Can
anybody provide any direction? I shudder at the thought of a complete
reinstall...

BTW, the system otherwise works fine. There is scads of free disk space
(over 100 GB on C:) and performance is fine.

(One other point: Acer includes its own system recovery software, called
e-recovery. I've used it to backup the restore partition, apps & drivers,
etc, so at least that much works fine. I do wonder, however, if somehow this
is conflicting with the built-in restore functionality in Windows...)
.