I purchased an 8oz popcorn machine off eBay last year... no brand name.. but the kettle doesn't seem to work anymore, every time I switch it on theres a loud bang accompanied by a loss of power (trips the kitchen circuit breaker!).

Although that said, the heating deck (that keeps the popcorn warm) and the halogen heating lamp still work.

I had given it a wash a few hours earlier.. I suspect some water may have got in there. I waited a couple days for it to dry out but the same thing happened. Any ideas?

The loud bang or pop noise indicates a direct electrical short and is possibly dangerous. Is the kitchen circuit breaker that is tripping a GFCI ? A GFCI breaker should trip before any loud bang or pop occurs. Needless to say..this most likely calls for removal of the kettle outer casing for inspection.
Be careful.