MY NEC 3540A only sometimes burn full speed!

Everytime I first burn a DVD when I just start my computer, it will work fine and burn in 16x. But the second and third time and so on, it will start off at 16x, then later it will go stight to 4x and stay there. It then would take me 15 min, EVEN tho it says its burning 16x!! I have upgraded to an 80 pin cable (nothing happened), checked the control pannel and stuff, I have a 1 gig of ram, and my cpu is not being fully used. Im using memorex 16x DVD-r. What could be wrong here. I’m using a fully updatd nero (and fully updated firmwire), and I also checked off high compatly dvd-r to see if that will fix it, nope it did not. need major help!

memorex, try better media. If you can find media made in japan.

Well I have like 70 memerex 16x dvd-r. Could there be any other problems?