Forgot gmail password and username to unlock phone HELP PLEASE

[#1]

so it goes the the screen where it says type  in your email and password to unlock. I dont even remember my username or password. Some people saytype "null" but it doesnt work... im willing to restart everything can anyone help me to reset this phone?!

[#2]

ok.... try going to the service centre and have them unlock it for you.

[Freda]

I tried holding the back key also and nothing happens,screen still won't unlock.Please somebody,anybody help.Its urgent.