Jacuzzi has been working fine for 15 years, but, something happened and the complete inside feels like it is made of sandpaper and must be a chemical reaction to ???. What caused this and abest way to fix??

This sounds like it could be the shaft seals, which is a cheap fix.
The Jacuzzi Magnum calls for seal 35-423-1021
You might consider replacing the seal plate O-Ring as well. - 35-105-1120

Depending on what the innards look like, you can spend $15 at a home center like Home Depot for a toilet replacement parts kit. They're easy to install (about 30 minutes) and fix most common toilet issues.

If this won't work you might need to contact a plumbing supply company in your area. You'd be surprised what they have in inventory....

I like "Gel-Gloss"....try that, if it does not work, contact the manufacturer...assuming it is acrylic, I would not touch it with sandpaper unless the manfacturer says to.

if the smell is very sweet something like peardrops, could be poystyrene packing. check for cable chaffing where it enters cabinet.replace mains cable completely. if mains cable outer cover is getting too hot it will smell as above WARNING polystyrene gives off cyanide gas over 120c/when burning do not inhale(only had 1 freezer melt in 30 years it was set on purpose)

Your Jacuzzi should be connected to a large GFI breaker. If it pops as soon as you turn something on, there is an imbalance between the legs supplying the power to your device. When my (small "J") jacuzzi (at about age 15) did this, I discovered a small leak that had dripped onto the circuit board and had left a deposit causing a "short". I was able to clean the deposit off of the board physically, I fixed the leak and return my tub to service.

The GFI is very sensitive and for good reason. It protects you from dangerous electric voltages, even though the danger is low.

Keep giving it a few kicks! When that happens to motors it usually means that it is on its way out, I'd milk it for as long as possible but start thinking about a new pump and motor.

use a color back wax found in auto parts store to restore

all heaters have a thermostat (or multiple) and heating elements. 
Start by removing the elements and seeing if they are burnt through.  If so, replace. 
If they look fine then replace the thermostat(s).
Both are relatively easy and cheap to perform.
Remember to turn off the power and water to the heater and drain the unit completely before doing any servicing.

autozone has a chemical called blue magic that works pretty well, just use some really fine sandpaper and buff it with some blue majuc

this problem of yours is something happen inside your psp try to go to a mechanic for psp he might fix it