1) Check device manager. Windows sometimes sets a drives DMA to PIO, which will result in a verrrrry slow burn. Reset the drive controller back to DMA & reboot.
2) It is possible your cd/dvd burner is going out. After they have been used a lot, they get "iffy", meaning sometimes they will burn, & other times they will not.
3) Check your media. If your burner is a 24x dvd writer, for example, then it may have problems writing to 8x "cheap" media. Try another cd or dvd brand. Some drives to not do as good with certain dye layers, so switching brands may help.
4) Check other burning software out, such as Infra-recorder or Nero to verify if they burn fast or slow.
5) Do a clean install of windows. You may be infested with malware or viruses, which can cause slow burns.
6) Tiger Direct has some P4 3,200 MHZ machines with 1GB DDR ram + 80 GB (7,200 rpm) harddisks & Win XP Pro w/SP3 for $303 something, which includes S/H & Taxes. Your PC may be outliving its shelflife, hobbling along on a scant P2 or P3 processor.
7) Check your mem. You may be trying to barebones your PC at 64 or 128 MB ram. You need at LEAST 512 mb for optimum performance on a system running XP or Vista.
8) Check how you are burning the disk. You may be doing something really dumb, like trying to burn direct to one drive while reading from another. It is far better to get a clean image to the harddisk first, then burn since you know if it gets a clean image to the harddisk, it will burn at max possible speed with no read errors.
9) Check your AV. Some AV products have problems with certain programs because of how they run. Disable AV solutions temporarily.
10) Boot into safe mode & see if you can burn. Booting into safemode will stop a lot of startup items that may cause problems from loading. If unable to burn, see if it will do a simulate burn.
11) I think this covers most anything that could have happened. I have used IMG Burn & it burns as fast as any commercial program does in my use. Of course, I do have a fast system that can keep up as well.