Please include more details about your installation.
Did you make some kind of backup that can restore you to where you were before the Win 10 install?
What is the make and novel of your PC? Laptop? Desktop? AMD?
What versions of Windows 7 did you use? It matters.
Do you have another working PC?
Do you have an ISO of Windows 10?
Microsoft offers free Windows ISO files — if you know where to look.
How to Download Windows 10, 7, 8, and 8.1 Install Media ...Yes, it is legal. You can make a Windows install media to either repair the installation or do a fresh install. You then will have a limited time to do the activation or otherwise get a license for Windows 10.
If the trouble PC does not work well with Windows 10, you should revert back to windows 7. In a few cases the Windows 10 drivers are not exactly right for some chip sets. This was said about AMD machines.
Bu I do not have any exact information about hat. EDIT: New post about Intel chip set trouble.
http://www.tomshardware.com/forum/id-2801754/windows-intel-chipset.html