Nozza brought next idea :

Now I can't close the garage door. It gets nearly to the floor - about
15 cms away - and is sticking out a little bit. Have tried pushing it
back up and trying again. Noticed theres a bit of dangly wire on the
left side, and the wire on the right is taught and now theres none on
the "rolly bit" at the top.

Tension wire snapped, or lifted out of its roller?

Secondly, what sort of price would I be looking at if I need a new
door/door mechanism, and how much are the electric rollery type doors
to get installed?

I bought one from a S****horpe company and installed it myself, to
replace an up and over type. It was made to measure and cost me around
£500 - electric and with 2x remote controls. I think I would have
rather tackled the install of the electric one than the up and over
type, it was much less fidley to align. I managed it alone, but it does
really need at least two maybe three to maneuver the door roll into
place. I was able to add a third manual set of button controls inside
the garage.

You fit two U shaped slides each side of the opening, fit the roller
including motor above the door, then lift the bottom end of the door
over the top and lower it down the slides. The motor is a tubular one
in the centre spindle of the roller.

The door slats are aluminium filled with insulation foam and the entire
thing seals pretty well, so it is much warmer /draft free than before.

To answer a question before it is asked...

If the power fails there is included a manual cranking handle to
operate the door, but the type supplied needs you to be able to get
inside to operate the crank. At extra cost you can get a crank system
which can be operated from outside the garage, if your only way in is
via the big front door. Not a problem for me because I have three
entrance doors into my garage.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk