Re: Windows won't start!
As above, if reformatting doesn't help then it's a hardware problem somewhere along the line. However, I'm pretty sure reformatting would fix it.
Here's the crunch, I could spent days or weeks taking you through different system files, possible outcomes if they're missing or corrupt, how to restore them, what parts of windows do what and then there's a possibility it might be back up and running as it was before.
...or you could wipe it, reinstall it and have a squeaky clean new windows installation to boot in an afternoon at most.
So you can see why pretty much everyone is saying reformat!