Did you try reseating the entire card? Maybe cleaning the part that sits in the slot?
Had my GVP die also once and it kept the entire Amiga from booting after pulling it out and putting it back in its worked flawlessly.
Best way to clean (IMHO) is the clean the card contacts with a rubber eraser to remove any oxidation and crud, then wipe with alcohol. The slots themselves can be cleaned with a stiff plastic toothbrush, then using an alcohol swap/pad wipe down the slot because everything should be a 2-step process; it also may clean out the dried toothpaste if you used the wrong toothbrush, although your slots might be minty fresh!
