Why wont my K5 Blazer start?it trys but wont.?

my 80' blazer will not start it has been startin up just fine.but today when i finally got my rearend put in it and new wheels and tires on it, it wont start.it turns over and tries to start but it stops at that.i have recently changed some stuff on my battery.its a battery that just has studs comin out of the top.on the positive one i have a screw on post and on the negative i have side post style.it was starting up fine b4 i did that could that be my problem.i checked the fuel filter and its got gas in it.i took it off and i could blow threw it.i dont know what to do.its makin me mad that i just put all this money in this truck and now it wont start for me when its done.if u have any suggestions please let me know.