Here are a couple of links to what I consider some good info on grounding probes & GFCI devices. Personally I don't use a grounding probe, but do use GFCI devices for all my tank equipment, more than one for redundancy.
http://angel-strike.com/aquarium/GFI...alDetails.html
http://angel-strike.com/aquarium/GroundingProbes.html
I also agree with some of the points wingedfish brought up. It sounds like wherever you had your grounding probe attached, there is a problem. If it was a ground on a wall receptacle, it wouldn't be a bad idea to get hold of one of those receptacle testers available at most reno centers these days. This handy little device will tell you right away if one of your receptacles is improperly wired or has a bad/missing ground.