Win7 clean install random restarts. HELP?

Just upgraded my system and did a clean install of windows 7. I noticed that after the computer is left on for a few hours it will restart randomly. When it restarts I get a message stating the following:

isolinux 3.20 2006-08-26 copy right 1994-2005 H peter anvin
A bootable dvd/cd is detedted press eneter to boot from the dvd/cd
if no key is pressed within 5 sec, the system will boot from next priority device automoatically
reboot and select proper boot device or insert boot media in selected boot device and press a key


Any ideas? The hard drive is the main boot device, the dvd is the secondary. Any help would be greatly appreciated.