XP hangs at Loading Bar

I am in the UK and in my house we have an old key charge system for electricity, you charge the key at the local shop and put the key into the meter until it runs out. Anyway, I left my PC on during last night and woke up today to find that the charge had indeed run out and electricity had gotten cut off so I charged it and booted up my PC and it just froze at the Windows XP loading bar, no respone to the keyboard (pressing Num Lock) and no response to the Power/Restart button so after waiting for 15 or so minutes I had to switch it off at the plug and power it up again. I got to the advanced bootup screen and tried all the options including Last known good configuration but only Safe Mode actually gets passed the loading bar screen (Actually it doesn't have a loading screen while booting up)...

Me, having very little computer knowledge talked to a friend of mine but he couldn't help much but he pointed me to this site and told me to ask for help here.

Windows XP
Service Pack 2
Pentium 4 2.8 Ghz
512 RAM

I don't know what other specs to post so if anything else is required just tell me.