magnum 350 trouble (u got a magmun take a look)

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I have got a magnum 350 had problems with it so got a new canister and an impeller assembly witched solved the problem now i have moved it from my 45 gallon tank to my 75 gallon tank (was off for 1 month totally dry in the bottom of the 75 gallon tanks stand) now it turns on and will run fine when it is not pumping water (in other words the quick valves are shut) when it attempts to pump water all it does is make a horrid noise and will not pump (have cleaned it no scraches on the canister there is a pretty bad scrach an the impeller magnet though) is it hopless should i take it out back and smash it? or is there hope