A Model Number would help

Cannot find any info using this Model Number, c'est la vie

You posted two different problems
Does not clean. Do you mean there is still food on the dishes?
Soap scum residue. Has it always done this or is it something that has just started lately?
Is it soap scum or is it mineral deposits. Vinegar will dissolve mineral deposits. A sign of hard water or poor detergent.

The most common causes of poor wash are:
1, Clogged filters or debris in the sump/pump area
2. Low water level, most units fill to just below the heating element.
This is often cause by a partially clogged filter screen on the input side of the water inlet valve. If this is the problem clean it, do not remove it. It is there to keep crud out of the valve which could hold the valve open and cause a flood.

Here is a good link with additional help
http://www.applianceaid.com/dishwash.html