How come my Window's laptop wont start?

Just before it started acting up, it started to get really slow. Like ultimate lag slow. I tried to ctrl+alt+delete. Then it just got stuck in the loading faze so i just powered off my computer. The next thing i knew i was getting this error message saying "Windows failed to start. A recent hardware or softwhere change might be the problem..." I don't think i got a virus since i wasn't on the internet. Please help me because if i have to bring my computer to the shop a 3rd time im going to spaz out.