Computer rebooting at shutdown

After a power supply failure about a month ago on my HP Pavilion desktop, I had a new power supply installed. After this, my computer would restart after running the shutdown program. I worked around this by disabling "Automatically Restart" under "System Failure" in the Startup and Recovery menu. This worked for a while, now the computer is restarting again on shutdown even though the "Automatically Restart" is unchecked. What is the problem and is there an "easy" fix? I have Windows XP home edition as an OS. Thanks.

 

Do you have any minidumps located under c:\windodws\minidump? If so, can you attach the latest one here?