Burning dvd on a mac os x

I have a Mac OS X 10.5.7
Processor 2.8 GHz Intel 2 Core Duo
Memory 2 GB 800 MHz DDR2 SDRAM

I can play burned dvd’s and pre-recorded DVD’s on my Mac but when I go to burn I get the following messages
“The disc can’t be burned because the device failed to calibrate the laser power level for this media.”
“Burning the disc failed because an unexpected error occured (error code 0X8002006E.”

When a blank disc is loaded the Mac makes a few noises and ejects the disc.
I use Verbatim 16X and was advised that my Mac can only take 8X. I have tried TDK 1-16X and it is accepted and shows on the screen as “untitled dvd” but when I transfer the chapters to the “untitled dvd” it goes through all the processes and the dvd ejects. When I go to replay nothing happens and the disc ejects.

I hope the above is not too convoluted and somebody can assist before I take it in to be serviced.

Thanks in advance