We use the Cascade tablets but they don't dissolve

make sure you have soap

Your soap tray and/or inlet is probably blocked with undissolved powder. Remove the tray and clean it. Also clean the inlet tube from the tray into the washing machine with hot water.
I, personally don't like soap powder and use a liquid or tablets because washers nowadays tend to use cold water only so doesn't fully dissolve the powder. Also the outlet to drain gets blocked along with the underground pipe to the mains sewage.

Find out whether your quick cycle is a wash cycle or a rinse only. If it is a wash it's obviously too short, and the tablet is not dissolving. You do not want undissolved tablets because they will contaminate your rinse water and u end up with soap on the dishes. You can switch to powder if a tablet isn't going to dissolve quick enough on your quick cycle.

The most likely causes are the you are using a tablet in a gel coating but putting the tablets into the dispenser drawer when the dispencer drawer is damp, thus causing the tablet to stick inside the housing; or, if the dispenser drawer is releasing the tablet into the bottom of the cabinet then I would say you have a problem with your water heater. In which case you would need an enginner to come and replace the heater.

Hope this is of help

I cannot tell you why your tablet doesn't clean well not knowing your machine, but having tried several types and brands (liquid, tablet, powder) I have found that the powder cleans best in my machine. Maybe it is something to do with dissolving or your water is not hot enough --possibly tablets work best in certain machines and not others. I don't have any interests behind my advice, but Cascade Complete was the one recommended to me and has become what I use exclusively. But I am willing to try others as technology develops.

I had the same problem and my wife fived it by unsticking a valve to the left side of machine in front lets water in she poped it open and dried soapm came out restarted and now works fine.

you can patch the crack/hole with a one minute marine epoxy. It works great. Regarding the fact that the tablet won't dissolve, you may wish to try a different dishwasher tablet or powder. You may also have another problem with your machine. Are your dishes coming out clean?

Having the dishwasher powder failing to dissolve is a far more common problem recently with the filing economy.  People are trying to save money by buying generic dishwasher powder rather than brand name products.  The ultra-cheap products fail to dissolve because their ingredients include bulk fillers with minerals, etc.
It is possible that the dispenser is failing to open, but that is a generally rare problem except on very, very old dishwashers. Before deciding the dishwasher has failed, go buy a box of brand name (Electrosol or Cascade) dishwasher detergent powder and only use it.
Please report back your results here, OK?  Good Luck!

Recommend you stop using the gel and switch to a brand name powder - like Electrosol or Cascade. Never use gel, gel packs or tablets in any dishwasher. Avoid untra-cheap, generic powders.
If problems continue, a service call, with them checking that the heating element is working is the follow up step.
Good Luck!

You don;t list the make and model number or its aproximate age.
The simpelest cause is switching to an ultra-cheap dry detergent. Recommed you use a name brand powder (like Electrosol or Cascade) Never use gel or tablets, ever.
Check all spray arms for blockages. Now is a good time to remove the filter (non trivial but do-able on most dishwashers.)
Clean empty dishwasher by filling a bowl or large cup with white vinegar and placing it in the dish rack. Run a short cycle with no detergent added. You may need to repeat.
If problems persist, the pump motor is probably failing. Schedule a service call or consider replacement of DW. Good Luck!