If you are uncomfortable with your own skills, go buy a new one.
I ran into this problem on the second use of my Pressure Washer Surface Cleaner.
In my case it's a simple fix. I have a properly sized Surface Cleaner. The pump is 2000 PSI, the Disc is 2000 PSI maximum.
Symptoms were when I got water to the cleaner, it spun a few times, then stopped while pushing water out of the nozzles under the disc. Stopping and starting the flow might get a few spins but it was not going to spin past that.
Before you proceed, make certain that all your water lines and filters are free and clean of any grit.
The fix for me was to disassemble the mechanism, clean it, use some light lube on it, and reassemble it.
The mechanism was held in place by a brass bolt with channels for the water to go through and "rubber" O Rings to keep the water from leaking out.
The shaft went out in two directions from the center to the nozzle. My nozzles can be removed and cleaned by removing the "silver" clips from the ends and washing them in warm soapy water.
In my case, the center shaft was the problem. I had to clean it, and the white plastic washer, of any sand and grit.
Remember: "Lefty Loosey, Righty Tighty".
Once you have the bolt in your hand, wash in warm soapy water, along with the washer.
The impeller arm in the center has surfaces that will need to be cleaned in the same manner, either with a brush, towel, or dipping into that soapy water.
Remove each piece from the water and clean them to remove any old grease or dirt.
I lubricated the white plastic washer with a little tri-flow because it felt like there was a lube on the mechanism when I took it all apart the first time. I used the tri-flow because I have used it many times on my skate parts, and it was on hand, but you may use your judgement on that.
You will want to use a light oil here because once you have done your surface cleaning, it will wash out. In this case, that is a benefit, because the servicing is so easy. Tri-Flow does not stay put on my skate bearings when they get wet, and they won't stay on this mechanism after a use - and that is the behavior you want.
Reassemble the mechanism the same way you took it all apart.