ULtra's psu sucks
the psu basically charges everything, if you have random reboots and your computer shuts down, its most likely a overheating or psu issue. The psu will also affect or effect your overclockign abilites, if it cant supply enough juice for the processor your processor obviously isnt going to overclock, and if you have a lot of hdds optical drives, you need a lot more power to go to those too while also powering your fans lights and other stuff.
read Ste. Psu section in the WHAT TO LOOK FOR WHEN BUYING A COMPUTER
at the top in the high performance section
AIM/Xfire - pzerofgh