Event viewer...

You say that Chkdsk didn't work, did you initiate it, and it didn't run, or is it just not fixing this problem even though it seems to go through the motions?

What is the blue screen error? May have to turn off auto reboot in system properties under startup and recovery. If you know when it is going to reboot be there when it happens, and you can get it back online once you record the BS error.

What else is running on the server, application wise?

SP level, hotfixes up to date?