sparatic power to fuel pump

this is my first post to the forum. i have read a ton on here over time and love the source all of you provide. i searched for this info and am hoping that someone can help me. my 99 blazer LS would not start for me the other day. it was warm cuz i just stopped at the store and came out and no start. the fuel pump was making no noise. so when i got it home i unscrewed the line going into the fuel filter and hit the key and no gas. after reading all the problems with these fuel pumps i picked one up today and was getting ready to install it. before that i thought i would be wise and crawl underneath and have my wife hit the key. all of a sudden the fuel pump has power and is working. the fuel filter was still unhooked at the time and i got a nice gas bath.

so here is my question: why on earth would the fuel pump have power now after sitting for a day? could it be a relay? the battery is new and so is the altanator. all i can think of is a faulty relay. please help. i really dont want this to happen to my wife while she is driving. or me for that matter!

Connection is bad or your pump is near death.