problems with start up

I would be grateful if you could offer advice. Whilst surfing the other day I received a message from a free piece of virus software alerting me to a file. I was not sure what this was so clicked to quarantine it. The PC continued to work fine until I shut down and came to restart. The start up now seems to be stuck in a loop. I have a Dell PC and it asks me to choose the operating system which I do, it then proceeds to the windows start up screen for a few seconds and then returns to the choose operating system screen. I wondered whether I have quarantined a file that was required for the start up. Can you offer any suggestions?

I have tried safe mode, start windows normally etc they are all stuck in the loop.