Since I have similar problems with my 708A I was searching the internet for discussions about this and found the topic here.
My first plextor 708A also stopped initialising cd media, but it did read and write dvd still correct. I troubleshooted the issue using different methodes like removing my SiS IDE drivers and run the drive on standard windows IDE ones, I restored my Installation image of windows being sure no program conflicts were there, I installed win98 as dual boot next to XP to check on a different OS, I updated the firmware from 0.1 to 0.3 that time and even tested the drive in another pc, but I couldnt get the cd function to work anymore.
I did send the drive back to them and got brand new one, a version 0.3 from december 2003. Now again from one moment to another the same problem occures and it doesnt read or write any cd media anymore. I dont think getting a new drive again will be a solution anymore. Maybe there is just something in my pc that this drive cant handle and destroyes its functions.
Also with the new drive I had writing problems for dvd mode (to slow acces time from hardrive even) , but they solved after getting the latest drivers directly from SiS site instead of the drivers that were provided by my mainboards manufactor, ASUS, for that chipset.
I can not remember the first time what caused the drive to not read cds anymore but with the second one now, everything worked fine until I wanted to burn a specific ISO to a CD/RW. I was erasing a formerly burned cdrw with Nero but when it didnt erase correct and the data was still there, I got another new blanc cdrw. I tried to burn the image (ISO) to the cdrw and after started it stopped immediatly with the power calibration error.
I rebooted and tried again in win98 using the official Nero release that came with the drive and the same error occured. After that I could not read or write any cd media anymore.
Later I realized that I had tried to erase the cdrw media in dvd mode in Nero, so that is why the first cdrw I wanted to use didnt erase correctly and I got a new one. Maybe this got something to do with the problem that have occured now and the cd fuction of the drive doesnt work anymore... But that shouldnt be crucial for corrupting your hardware i should say, only the media.
I dont know what it is, but I'm afraid getting a new drive again will end up in the same soon or later. Is it my computer hardware that conflicts the drive? Or is it a bad production set from wich I got the drives...
Did it happen coincedently or did it happen due to a software action I performed....One thing is for sure, this should not happen to a drive due to some program's function and even more when it happened with the official software included (Nero 5) My second drive is just again tachnically defect again, and no firmware update or configuration will help anymore. Im sure they will offer me a new one, but I that wouldnt help. This 708a is just to sensitive for specific actions and soon or late this will happen to you to if you have 708 bought between the first release and now, unless the fixed it as of now.
Maybe you could list some details too about your system hardware and what you have done with the drive in wich software and when the problem occured. I did before burned a nd erased several cd discs though until it happened to the cd function of the drive. So im not sure if it just happened coincently or due to something. DVD reading a writing is still okay.