716A and plextools issues

I RMA’d my first 716A about a month ago, all was fine with the replacement until now but things seem to be going downhill again already. When I first got the replacement if I put a blank CD or DVD in the drive you could hear the drive spin up and it would open an (empty) window, now when I put a disc in it doesn’t seem to spin up and the window doesn’t open. Also if you hover the mouse pointer over the drive in ‘My Computer’ it shows a blank disc as 0 bytes used and 0 bytes free (whereas my other drive a Pioneer 105 shows 0 bytes used and 702MB free). Just lately I’ve noticed it’s taking 13 minutes or so to write a dvdr at 8x speed as well.
Also I have had no end of problems with plextools (old and latest versions) whereby when I put a disc in, plextools will start using approx 50% of the CPU (P4 2.6Ghz btw) and the only way to kill it is to kill the process in the windows task manager.
The last RMA experience was very favourable (send on Wednesday to Belgium, new drive arrived on Friday) but I’ve pretty much given up hope now that I’m going to get a reliable burner from plextor and am thinking of just getting the new LG 4167 instead.
When I insert a blank disc should I be able to hear it spin up and should it open a blank window or does anyone else’s behave like mine? If I open dvd decrypter it shows the correct space free but it’s the fact it doesn’t seem to do anything when I put a disc in that’s worrying me (as well as the fact it only seems to write at 4x when I set it to write at 8x).

Thanks,
Andy.

Have you checked to make sure that the drive is operating in DMA mode and not PIO?

Yeah, it’s in DMA mode 4.