car is making me mad

[DisEpyon]

hello,
this is for a sr20det s13

i need some help, and i ran out of ideas on what it could be.
my problem is my car wont start (not turning over, not cranking). it makes a fast clicking sound.

it all happend when i was swaping out my differential with a welded one. my car has been sitting in cold weather for about a week before i got everything back together to figure out that its not starting. (took me a weeks cause i had a vicous drive shaft and it is shorter than a normal one, before i found one)

I took the starter off and had it tested at pep boys and it was bad, so i took it to a near by starter and alternator repair shop. got it today and put it on and same thing happend. fast clicking. the starter was going bad because i remember a couple weeks ago that after starting my car there was a grinding sound coming from the transmission, it was the starter.

ive tryed jump starting my car with another car, and nothing. checked fuses and they look fine. checked all ground and connections and looked fine, except my main ground battery connection im not to sure of, battery been relocated to the back. but i did this about month and a half ago, so i dont see a reason on why that would matter now. everything on my car works but wont start. im getting fuel, pressure guage is getting it, cd player works, fan works.
I recently bought a optima battery about a month ago, ive charged it overnight and that didnt matter. im not sure if its that or not.
please help me, this is a dayly driver car and i want to drive badly.
thanks, brent