sticky or broken home button iPhone 4 GSM

help!!! i have always been a fan of apple, had numerous iphones & ipods, at some point these have been broken and ive repaired cause apple take so long! my 4s was stolen so i bought a 16gb 4 GSM from a friend, i had it matter of 30mins max and dropped it, smashed front glass/digitizer! so i replaced it with oem parts, before the home button was fine! but now when i press the home button it sticks down and then voice control comes up if it dont stick down it doesnt work at all so i press it a few times to sorta force it to work and then multitasking comes up, i litterally cant get back to the springboard unless i turn phone off then on again! ive taken the phone appart clean the HB connections and clean the HB itself but problem still there!! can anyone help?? will i need a new home button or is there a way to fix this?