Microsoft changed the licensing terms for windows8 and hance your PC goes with a Digital product key.
Most consumer notebooks are not designed for windows7.
Even if you downgrade, you may not be able to get some core functionalities to work.
If you do not like the Windows8 user interface [read: start screen], You can always install a windows 7 shell, that will change the way windows8 looks and make it look like windows7.
The most popular around the web is called as "Classic Shell". you can google that and install it on your PC.