There are several things that could have happened to cause the reset including a power drop out or spike. The real question is why Quicktime and iTunes are not working after an erase and install. Assuming you followed the normal procedure of running Software update after the reinstall to update all your applications to the latest version and repairing permissions, the first suspect on my list would be RAM.
Get the freeware utility
Memtest or if you prefer the GUI version
Rember and run it for a minimum of five complete test cycles to see if there are possible memory problems.
NOTE: depending on the speed of your Mac and how much RAM you have this can take several hours to complete -- you might start it before going to bed at night and hopefully it will complete by the time you get up the next morning.