If your belt seems to be ok, ( £2.99 from local shop, with 2 pages of instructions for taking off and putting on,) I have had most success by putting only water in the detergent dispenser- it needs something in or it won't work, and putting the detergent in with the clean hot underline hot water . Using this method I have managed to do one room, woopee.
I have to say it worked well. If you visit the bissell website, or look at the instructions, there are hints like, leave the machine standing for a minute after changing water or detergent, so that any air can find it's way out. This helps with the frustration of 'It's stopped working again.'
Let us know how you are doing.
good luck
Diy-jim, August 2006