Help needed, I've broken my site!!

Hi
I'm currently running 1.5.4 on my domain sunplastics.co.uk/buy

On attempting to upgrade to 2.0 (after making full backups) - it didn't work, so decided to revert back to original installation.

However, now I'm presented with a blank screen on home page, and a very broken looking admin login page.

Having trawled the forums, I just can't seem to put it right!

Can anyone help?

did you put the database back when you revert?