Doesnt boot

On pressing the start button, It goes okay till showing the xp logo and asks to start windows normally or in safe mode etc. Then a blue screen appears asking something abut check for viruses..... N then it starts all over again. What shud I do??? I don't have the win xp cd for formatting

Hello everyone! i have a problem with my notebook Aspire 5625G. I have it quiet longer now and all i did on it was changed hard disk. Then it runned for some while. And now i have a problem that i dont know what to do with. The notebook sometimes did turn on. like after 5 times of turning it on...