when i looked up that philips drive, the first hits were for problems recongnizing discs. it might actually be the drive itself.
also, it says it only a +R drive, so make sure you only use +R/W media, not -R/W
Philips DVD8421 supports DVD+R/RW and DVD+R DL, but not DVD-R/RW. It is not a dual-format drive, and cannot burn DVD-R discs.
the asus one just looks a cd-rom drive.