big time help please

I have a 95 3.8 which was overheating. Checked it out and found the head
gaskets to be the fault. I replaced the head gaskets, put everything back
together as well as I could, now...it won't start. Started the first time
after gas starting running good, got clatter from the rocker arms, but
now it wont start. The only thing I know that I did, in not keeping with
good order, was that I didn't replace the injectors where they came out of.
I just put them in anywhere. Could this cause it not to run. I'm really in
bad shape. Need help. Didn't touch the timing at all except for
disconnecting all the electrical sensors but plugged them in again without
moving anything.

Help..................

hey guys, when I say that I put the injectors "anywhere", I just mean that
I didn't put the #1 injector back with the #1 cylinder, etc. I just dont know
if the injectors are somehow synchronized with their respective cylinders
or not. Also when it sounds like it wants to start, I get a big "thump", like
it was out of timing. Don't know what to do next. any help will be greatly
appreciated.