PC getting random reboots and shut downs. Please help!

[Sewei]

Hi, I'm a new user here. Anyway back to my problem.
So a week ago, I brought my computer to my friend's house to LAN. On my way there, I made the mistake of placing my computer vertically on the back seat. Throughout the ride, the computer shock back and forth, and feel on its side on a soft surface. After the lan, I noticed that on the second boot screen, when it is booting up the devices and what not, at the end, it says "Boot from CD:" two times. I ignored that for a while seeing how it seemed trivial, but I accidently kick my computer gently forward, moving it accidently while it was on. The computer turns off with no BSOD or anything. I open my case and make sure all the hardware is tightened and all the plugs were at the right place, finding nothing unusal. I ignored it till today, when I plugged in my Zune into my computer, moving it a little trying to plug it into my USB slot. I do that, and the computer all of the sudden reboots. This had never happened to me before, and I never had the problem of random reboots.
I figure this may be due to my harddrive moving back in forth in the car, and I want to check If I damaged it. Is there any software that scans to see if your HDD is fine. Also, I would like to see your thoughts and suggestions on what is wrong with my computer.
Thanks in advance.

 

[evongugg]

Your computer is probably fine.
if you go to the manufacturer's site you can download hard disk diagnostics for your hard disk. You can also run the Hitachi hard drive fitness test.
The reboot could be due to the power supply or to defective memory.
For memory you can run memtest86+.
If this is an isolated incident, don't worry about it.