Whilst loading minecraft it crashes

I click play on my minecraft and it loads as thought it is going to come onto the minecraft page where I select singleplayer and multiplayer but goes back onto where it says play and says "crash report"
I am not sure what the problem is, I did a system restore a few days ago to set my computer back because it was running slow so I wanted to make it faster but it worked once after that now I came on today and it keeps crashing, if you could let me know as soon as possible how to find out the solution or the problem to this crash that would be brilliant thanks!