Why my computer wont start windows 7 after uninstallig windows 10?

[Windows Central Question]

I downloaded windows 10 to my computer which has windows 7 Home premium but after I installed windows 10 start menu didn't work at all and it slowed down my computer. So I decided to downgrade back to my windows 7 but after the downgrade was done my computer was unable to start windows... I made the start up repair cuople times and I can't restore my system to previous configuration point. So what should I do.. Is my computer gone because windows 10? And my computer is a laptop; Asus x53s