Backing Up Your Computer

I don't understand there are times when I open my computer it crashed even I didn't open a website yet. Now, I started to think that my computer has a virus which I don't have any idea where I get from. I am very concerned about all my stuff I had downloaded and uploaded in my computer that may result to loosing all of them. I don't want it to happen you know. I think the best idea is to get an online backup to make sure whenever my computer crash again I can restore all the stuff that I have saved for few years.