Sand-blasting cabinets?

Guys, I need a little help. I bought the table top cabinet from Harbor Freight, it was on sale & I could not pass it up. It should be good for learning & seeing how much I use it. I have it all set up, over-caulked all the seams, added a light, hooked up my shop vac, ran the air line into the gun. I filled the bottom with aluminum oxide 80 grit for some suspension parts I need to blast. Filled up the compressor & got everything started. When I squeeze the trigger, nothing but air comes out. The tube that hooks up to the gun is fully submerged. When I take it out & just spray the gun air comes out of the suction tube instead of it sucking air in. It seems fairly straight forward. What am I doing wrong? Is my compressor not strong enough to create the suction? The cabinet said 100 psi working pressure. My compressor fills to 130, has 10.2 cfms @90. It should be strong enough. Is it the gun that is supplied with the cabinet? I really do not have $60 to buy a new gun especially if that is not the problem. If the compressor is not strong enough than the cabinet needs to be returned because I can not buy a new compressor right now. I am leaning towards returning everything, getting a refund & just paying someone to blast the parts for me. Any help would be greatly appreciated. Thanks:banghead: