Dishwasher powder/tablet not being used

You don't put salt in a dishwasher unless you want to ruin it.

2. You ONLY use a detergent specifically for dishwasher use as the cleaning agent and you 3/4 fill the soap dispenser in the washer (normally fitted into the door on the inside) with the dishwasher powder.

3. If there is a separate small compartment in your dish washer for a "rinse aid" solution to be used, you can use a rinse aid product designed for dishwasher use only. If there is no rinse aid compartment (this is also normally fitted to the inside of the door - if fitted on your machine) then you cannot use a rinse aid in your washer.

4. Don't use any other product in the dish washer.

Likely not dishwasher tablets / powder are generally harsher than soap powder. It would not be a good practice to do constantly as detergents are formulated for specific purposes they vary in pH, surfactants and other agents that keep dirt in suspension so it can be rinsed away. The dishwasher cleaners really should be used periodically as every now and then it is good to run a wash the machine rather then it washing dishes.

Check inlet water quality. It's hardness level. Use salt meant for dish washers. There will be a salt fill compartment. Refer user guide.

Finally check whether the rinse aid dispenser has liquid for dispensing.

Five common causes:-

1. The dishwasher hasn't got any salt in, or the salt dispenser control is set too low. Even if your tablets/powder have a salt function, it's often not enough in hard water areas and supplementary salt must be added to the salt dispenser.

2. There is no rinse aid in the machine or the dispenser control is set too low. Supplementary rinse aid may be needed even with tablets/powder which claim to include it.

3. The dishwasher is not reaching the correct operating temperature. This can be due to a faulty machine, or by using low temperature washes inappropriately. Low temperature washes are only suited to very lightly soiled loads which have not baked/dried on. There ARE special low temperature tablets/powders, but they're designed only for specialised domestic machines with low temperature overnight wash cycles or for commercial dishwashers.

4. The filters/debris traps at the bottom of the machine are not clean.

5. You're using the "wrong" brand tablets/powder. In this instance "wrong" simply means that your machine just doesn't get on with the brand you're currently using. price has little to do with it; I find with my current machine that the market leading expensive brand works poorly but the ultra-cheap supermarket basic value brand works perfectly. Also it can be down to using a genuinely wrong tablet/powder choice as per suggestion #3.

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.

Yes, the wash arm should spin freely. Recommend that you remove the arms and search for what is stopping it.
In addition to hard water, the ultra-cheap dishwasher powder really does/can leave calcium-like deposits behind. Use brand name powder for 30 days and you will see a difference. Never use gel or tablets in any dishwasher.
Adding a whole-house water softener would eliminate 90 % of your problem. The other 10% will be taken care of by not buying ultra generic powder.

if that is a drawer dishwasher ck manual i believe it it says powder only the fp drawer dishwasher doesn't use much water so desn't have a lot of spray force to dissolve tablets

With the LG LDS5811 dishwasher and other water/energy saving dishwashers, they are VERY ineffective with untra cheap powder detergent. Switching to Electrosol or Cascade has solved the problem -- and don't use too much.
If you add a whole house water softener, you will be AMAZED how much better your dishwasher and clothes washer work -- especially if your cut down on the amount of detergent your use.
Oh, never use gel or tablets in your diswasher. Ever.
if the problem with the detergent dispenser not opening is a seperate problem. Recommend you submit a seperate problem/question.
Good Luck!

The low detergent light comes on because the dishwasher recognizes the powder or liquid wash detergent.

In the Tablet form the dishwasher things you do not have enough becasue the tablets are condensed tightly. I use the tablets and I ignore the low detergent light entirely. The tablet is good for ONE wash and is sufficient.

If your dishes are not coming clean, I recommend that you prewash or scrape dishes ahead of time.

If you live in a hard water area the 5 in 1 tablets will only work half way. Consider Calgon powder or the tablets which can be left in the dishwasher cutlery basket as an additional measure. Hard water areas are notorious for leaving chalky residue on cutlery regardless of 3 in 1/5 in 1 tablet promises. 
Also your dishwasher will require rinse aid too as most machines need this to mix in with the general water and soap solutions when the dishwasher is on its final rinse.