It seem the traffic depend on the max CPC. is it true?
If I set
max cpc .5$ ,daily budge 4000$, got traffic 21-26
"home theater system"
$0.34 - $0.50 4 - 6 21 - 26 $8 - $20
max cpc 1$,daily budge 4000$, got traffic 263-392
"home theater system"
$0.73 - $1.00 1 - 3 263 - 392 $200 - $400
what is the problem? to my know, traffic only depend the budge you set if your adwords is actived.

and another question.
how to optimize the ad compaign to activate my adwords? does it work to change the headline or description of ad to trigger my ad to show on ?

Yes, the traffic depends on your maximum CPC, since a higher CPC gives you a higher position (the formula is Conv Rate x Max CPC = Av. Position), so when you get a higher position you normally get higher volumes of traffic.