Never know if it will start

When I go to start my blazer sometimes it wont start and nothing will happen. Ill take out the key and try again and it will sound like the battery is dying and wont start. I will then try again and it will start righ up. I know that it cant be the battery or the alternator i just changed both of those two weeks ago. Has anyone else had this problem?

Ignition switch or starter are prime suspects. Cables and connections all clean and tight?

Have battery and charging system tested.
Also check for current draw with key off.
You may have something running the battery down.
MT

I had an issue like this and it turned out to be my sun visor lights were staying on all the time. I couldnt find replacement ones (because the plastic flip part on mine is broken) so I taped them so the lights will stay off.

Anyway back to the point,check all the possible suspects and even some you wouldnt think of.

Ignition switch or starter are prime suspects. Cables and connections all clean and tight?

I agree with above on both points. I would have said "switch AND starter"
If you turn the key to "on" and there's no lights on the cluster, change the ignition switch.
If you have a fully charged battery and the engine cranks slowly, your starter is on the way out.

This morning I tried to start and nothing I HAD TO JUMP START MY TRUCK 4 TIMES!!! BEFORE IT WOULD STAY RUNNING. Some times it starts still and some it doesnt. Im going to have it tested today hopefully Ill let you know.

YES!! It was the most annoying thing! Under completely random circumstances and at undpredicatble times, and NEVER when I took it to a mechanic. Do You have 2 sets of keys? Try using the other key for a while. That's what worked for me. It sounds silly, (mechanic briefly explained this to me) but there is a magnetized portion of the key, somtimes it reads correctly, somtimes not. all I can say it it cleared up my problem. P.S. when it was "not starting" it would start after waiting 10 minutes, so I never got stranded somewhere.