Okay, let us treat this as two different problems (which is what it is).
I can help with problem number one, the sudden loss of speed. Two of the replies above both spotted it (thanks to AKO and Geno888). Here is what your log showed:
=== Scsi-Device-Map ===
CdRomPeripheral : SONY DVD RW DW-D23A atapi Port 4 ID 0 DMA: On
CdRomPeripheral : SONY CD-RW CRX320E atapi Port 4 ID 1 DMA: Off
DiskPeripheral : WDC WD2000JB-00GVA0 atapi Port 5 ID 0 DMA: On
If the "slow" drive was this one --
*** CdRomPeripheral : SONY CD-RW CRX320E atapi Port 4 ID 1 DMA: Off -- ***
Then, look at the end of that line, where it says "DMA." It says "off." My guess is that it probably used to be set for DMA enabled (which is much much faster). Then, at some point you had a total of six "read" errors, such as "Cyclic Redundancy Checks" which are also called "CRC errors" or "check condition errors." When Windows gets the sixth error of this type on any hardware device, it automatically switches the device from DMA mode to PIO mode. It has been programmed to do this, assuming that your hardware might not be able to handle DMA mode. They never anticipated that dirty DVDs or dirty CDs would be causing so many errors. Windows does not tell you it is doing this, it just does it.
Solution--> Do a search, you can find info on how to resolve this. The version of Windows can make a slight difference as to which is the best approach. In some cases, you can just go into the hardware settings and change it (under the System Properties" and "hardware devices." In other versions, you have to uninstall the IEEE controller that is handling this device, and Windows will automatically re-install it as soon as you re-boot, and Windows will load it with DMA enabled again.
Microsoft has a tech paper in their knowledge base on this peculiarity.
You should also be able to find suggestions for how to resolve it by searching these forums, though.
Regarding problem number two, I shall leave that to someone else. I have no idea why you are unable to burn...