I am about to throw my computer out the window. Invalid System Disk

I came home from college a few weeks ago and installed Windows 7 to my parents desktop. About a week later, this error message came up on during start up: Invalid system disk. Replace the disk, and then press any key. I tried everything from repairing it. I eventually gave up and took it to Geek Squad. When I got there, (mysteriously) my power supply went bad so they replaced that, and then he decided to replace my hard drive. I took my computer back home and loaded Windows 7 from the disk I ordered from my University. Fast forward until today. I was messing with personalization when I realized that the Windows was going to expire in 28 days. That's when I noticed the Windows 7 I got from my school was upgrade only. So I popped in my original Windows Vista to the computer and proceed to do the installation. At one point, the install wasn't working right because I didn't partition a drive to allow the install to work. So I picked the new hard drive and proceeded. when the install forced reboot my computer, Invalid System Disk came up again. And to add, it now says: BOOT MGR is Missing. Press CTRL+ALT+DEL to restart. I have no clue what is going on, and I am thinking about lighting Best Buy on fire. Please help me out!

A little info about my computer Old Operating System - Windows Vista Home Premium 64 Bit New Operating System - Windows 7 Ultimate 64 Bit Old Hard Drive - Seagate Barracuda 750 GB New Hard Drive - Seagate Barracuda 500 GB

If you need any more info, let me know.