Alison, you don't say if the broken cooker hood actually has power. I think, but am not absolutely certain that your cooker hood should have an external fused isolation switch.
If you follow your drastic route of putting in a new hood you will do best to fix the external fusing issue at the same time.
If it were mine I would switch off all the power and wire the cooker hood supply cable to a lampholder with light bulb. Switch the flat's power back on and run round throwing every switch in sight until I could turn the bulb on and off. Then I'd learn which circuit the hood was on and possily the fusing arrangement.
At the same time I would examine the existing hood and temporarily wire it up to a known good supply for troubleshooting on bench, table or worktop - and fix it!
You will feel pretty silly if you buy a new hood and install it and discover that all the old one needed was a new 3A fuse hidden away at the back of a cupboard or underneath the base units behind a plinth board.
If there's a similar flat next door you might ask the people if they know where their fuse is.
Good luck...
Peccavi
July 2009