Black screen after animated window is usually device driver load problems .. Usually Graphics drivers or chance there is a memory problem (you would have been getting BSOD's) If you changed graphics drivers recently, you should try a restore point back when you know it was ok.

A defrag? Nonsense ... Wont do a bloody thing to help on startup .. The system finds the correct file in System32 folder, then away it goes.

A safe mode boot and chkdisk may also be helpful.

Ignore the MSconfig thing .. Thats not for XP. You use services.msc for that.

Download Hijack This and check for Spyware drivers loading up on start, they can also give an unresponsive boot

If you want hijack this from me, drop me a PM .. but you can find on line.
You dont need to be too drastic just yet : ) You need to show the hijack this log file to someone who knows about computers .. dont delete entries willy-nilly, or you will be reloading the OS

You could benefit from a decent registry cleaner, most do! You can fix a lot more than you would think when you go about it correctly.

One more thing .. If you have succesfully booted, you should clean out everything (incl folders) in Windows/Temp, C/Docs & Settings/Local Files/Temp This is all rubbish that has accumulated. Anything like Temp Internet file folders will be recreated by Windows if needed on reboot. Also clean out the cache .. C Panel/Internet Options/Temp Files/all content.

Good luck!