after the first set of any exercise i get to weak to do any more sets..what do i do?...do i do less numbers of reps on the second set?

What does your current set/rep scheme look like?

DM

i bench press 15 sets for 15 reps..

sorry i meant to say 2 sets and 15 reps..

If you are looking at getting stronger, then stay with 5 reps. To gain mass, go for 8-12 reps.
Make sure your diet is up to par and that you are not benching 3+ times a week.

Deae,

How long have you been working out? One set is great if you're just beginning. Try to complete as many as you can with good form, without over training yourself. You'll know when you can add more, don't over do it. Burning can sometime be a good thing as long as you don't over do it. Make sure you rest the next day too.

Necia