First blow it out with compressed air...
Preferably Compressed Air from a real air compressor and tank and an air drier.
With a ground strap connected to the case and a ground strap to earth ground
Remove the RAM... Then take a video tape cleaner "foam swab", and the head cleaner, swab out the sockets and the RAM. Then use sterile water (its non-conductive). Try not to get the water in the power supply
Eventually you'll want to get some electronic non-lubricating spray cleaner and clean the crap out of it. It should neutralize the ph from the urine.
Once you do that... let it dry a while (or blow it out, if you got water all over and let it dry a day or so)... and once you stop being buzzed, put it back together...
Power it on.