Creda Tumble dryer fixing the belt back on?

I am trying to fix the tumble dryer, basically the belt has snapped, so having undone the back of the dryer, and purchasing a new belt i have managed to get the belt onto the pully system and round the spindle... for some reason, it doesnt feel taught, however it looks like it should work.... problem is when i turn it on, the belt doesnt drive the pullies and the drum doesnt turn.... instead the belt rubs on the metal and smokes!!!!

What can be the problem?
Does it matter which side of the belt touches the drum, i,e ribbed or smooth? could that be it?
Please someone help, having got this far it would be a nightmare to call someone out now and pay all that money!

Cheers
Ade