have a virus and wont start

It's probably not a virus, this happens with phones when they have issues. Could be a hardware issue.

Easiest thing is to just bring it to a store of your service provider. If you want to try to fix it yourself, look up how to do a factory reset, it may help. If that does not help, you can look up how to download and flash a default ROM onto your phone. We're assuming it's an Android phone here.