We'll need more information to help diagnose the problem.
1. What type of resin?
2. What ratio did you pour at?
3. Was it mixed properly?
4. How old is the material?
A thing to do that MIGHT help kick the cure is to add heat. If you have a hot box or if it's nice and sunny outside, expose the mold to a little extra heat and see if that works. More often than not, if your material isn't curing it's either contaminated, or the mix ratio is off / not enough catalyst.
If this is a polyester resin and you didn't add hardner (I've done it before, it happens), no amount of heat or time will cure the resin.
To salvage the mold I'd wipe/pour out as much of the uncured resin as possible, then chase that with a batch of over catylized resin. Hopefully this can help kick off the sludge left in the mold, and you'll be able to pull most of it out when the second batch cures. If not, you may be stuck just cleaning the mold with the appropriate solvent, be it acetone, naptha, denatured alcohol, etc.