Windows 7: My Windows 7 OS is broken, NEED SERIOUS HELP!!

Hi, I was messing with Windows 7 themes(Like replacing Explorer.exe, shell.dll etc)..
Now my OS is f'ed up, everytime I log on and get these errors
Error #1.
Title:"AtBroker.exe - Application Error"
Message:"The application was unable to start correctly (0xc000007b). Click OK to close the application."
Error #2.
Title:"explorer.exe - Application Error"
Message:"The application was unable to start correctly (0xc000007b). Click OK to close the application."
And then the screen goes black and I only have a cursor. And taskmanager doesn't work I get this:
Title:"taskmgr - Application Error"
Message:"The application was unable to start correctly (0xc000007b). Click OK to close the application."

And stupid..Stupid me forgot to back-up explorer.exe

My computer is a Dell Latitude|E6410 Windows 7 Professional 64 bit, if that helps..

I would've format/reinstalled Windows 7 but I don't have the CD/License key, my dad gave me the pc, and it came with Windows 7 pre-installed.



And I don't want to call Microsoft, or get it repaired, my dad will kill me if he finds out..

PLEASE HELP!!

somewhere on that computer, I have no idea whether that's a laptop or desktop and your system specs do not say, either on the bottom or the side is a Certificate of Authority (COA) sticker.

That sticker has a number on it.

Do you find the sticker?

Do not tell us the number, just tell us if you found it.