Hey, ive got a 300w powered pa speaker. It has an imput for a mic and i can plug my guitar in dirrectly to speaker to get both cranking at the same time. But the amp died pretty quick as it makes a pretty bad crackling and popping noise and cant really be used. Is this a result of having 2 different inputs used at once or just a crappy speaker???

Please explain more!
Do you mean you had two different amps driving the same speaker?
If a speaker has two inputs it doesn't mean you can/should drive it from two different sources.
The other jack was for an extra speaker (are the jacks marked?).
If you short the outputs from two amps one of them will come out the winner...