i borrowed a laptop from a friend and it was locked, so i shut it down manually. when i rebooted, it got to the windows startup screen, and as soon as the bar fills, the screen flashes quickly and displays some sort of error message at the top and restarts it's too fast for me to read it, but i saw something about a system error. this will continue until i shutdown. any ideas? i know im being kind of vague, but im not good at this kind of thing

What you can do is bootup, sit with your finger ready on the "pause/break" key and as soon as the error message flashes up, hit the button. If you're quick enough, you can freeze it on the error message so you can record it. If you're successful, post the error msg here.