Well folks thanks for the tips.
I had the same scanner failure error on my HP Officejet which was a hardly used and fairly new printer so admittedly I was annoyed when it failed.
I tried all of the solutions on here and non worked - being honest problem appears to be more mechanical than power giberish. Fortunately I bought a new printer as one was for another room anyway so I thought; "what the hell. if brains won't work then maybe BRAWN will" so......
I bashed the plastic where the scanner had stopped on right hand side of the scanner, then in the middle of the left hand side on the scanner (glass/scanning section), theres a spindle so I tried turning this around with a big Allen Key in the direction it spun freely and then tried again. It didn't work so I thought..... EXPLETIVE ***^$** IT and turned it around the opposite way and heard a couple of crunches as I had nothing to lose as would bin the 4500 alltogether anyway.
Having had a good couple of crunches against the direction of the free spinning cogs (WARNING - don't overdo it 2-3 at most - no liabilty here if you break your own stuff)I turned the 4500 back on......
Result...... Orange Light, Gone, Error Message GONE.................4500 Works as good as new.