There are different versions of windows 7. When connected to the internet and you can't seem to activate windows check if your laptop/desktop has the windows key underneath, or behind your unit.
Every computer comes with it original keys to activate windows for when an accident happens with your hard drive you may reinstall your unit original operation system, and enter the key so then it will remain genuine.
Like i said before there are different versions of window7 such as, basic, pro and ultimate. You have to have the same windows7 version to enter your pc original keys. That again is located below or behind of your unit.
If either wont help you out, i have a program which activate any operation system. windows7 and below. If you need it, the program that i use, and is reliable is named "windowsloader"