I am working on a friends Presario 6300. It seems to be in a rebooting loop. I cannot boot into windows at all, including safe mode.
I finally was able to get into the "F8" section to disable the rebbot on error and came up with the following...

STOP: C0000139 {entry point not found} the procedure entry point rtlencodepointer could not be located in the dynamic link library ntdll.dll

I was unable to fins this error on a google search.
I had an extra Hd laying around and I was able to put WinXP onto this HD and hooked up the existing HD as a slave and was able to boot up. at that time I scanned for virus's and the HD came up clean.

I am about ready to completely reformat, unless someone has some advise.

Thanks