The cmos checksum error is well done. Did you try replacing the old battery and setting the BIOS settings then saving them? (sorry but that topic is rather well done.)
The all folders read only could be related but until the checksum issue is fixed I would NEVER work on the hard drive except to back it all up again.
Recently, I have been getting the following message on booting: CMOS checksum error; and then I found out all my folders had become read-only, and I couldn't change their properties. What could it be?
I have run AVG which did not detect anything.
My desktop (xpc) is running XP SP3