Windows 7 boot loop - Can't install from CD either...

Using a Dell Inspiron 1545 laptop that's about two years old.
I was previously running Vista and decided a few weeks ago to upgrade to Windows 7. Everything was working fine for about a week. One morning I turn on my computer and I find a dialogue window saying that Windows has detected that I was not running a genuine copy of Windows 7 (not true.) My desktop wallpaper was gone, replaced with a black background with a similar message in the bottom right corner.
I immediately started having performance issues. Specifically, a few second after turning on my computer, the screen would go dim, almost black. I could barely make out the same dialogue box that I described earlier. I would have to reboot my computer until the dimming issue went away.
After about a week of this, Windows would not boot at all. Initially, I will get a screen giving me the option of "Launch Startup Repair" and "Start Windows Normally." If I choose startup repair, I'll get the screen that says "Windows is loading files..." at the bottom. Immediately after, it looks like Windows is booting, and then the screen goes black.
If I choose "Start Windows Normally," I get the "Starting Windows" screen with the Windows 7 logo, and after about thirty seconds, the computer reboots.
I've tried to reinstall Windows from my original disc. After the "loading files" screen, I get the Windows boot screen, followed by a black screen 30 seconds later.
I cannot start the computer in safe mode. I cannot start the computer from the last known good configuration. Either of these options end up the same way.
I've reset the bios, no dice.
Does anyone have any additional suggestions? I'm not incredibly computer saavy, just as a heads up.

Thanks in advance for any help.

How did you upgrade?

I used a windows 7 disc that my roommate bought from his college bookstore.

So he used it also?

Did you activate it with the Product Key on COA sticker. Are you sure you're the only one using the Key?

If so try reactivating at Control Panel>System link or in the bottom right System tray.

If unavailable wipe the HD with Diskpart Clean Command using DVD accessing DISKPART At PC Startup , then clean reinstall.

You can copy out your files to external or USB flash stick using 7 DVD or System Repair Disk this way: Copy & Paste - in Windows Recovery Console,
or use Paragon rescue disk; recover data

If you can't boot into DVD to copy out files use the Paragon disk which will autostart itself, then boot free Partition Wizard bootable CD which will also autostart itself to Wipe the HD from Disk tab, after you click on Disk # to highlight it. This will force the install DVD to autostart too.