Seagate HD Not Setting DMA Mode

XP Home, Asus P4C800-E MB, 2 hard drives on IDE 1: both work fine at UDMA 6.Second IDE has my DVD burner in the master position and works fine at UDMA 4.I'm using the proper cable, plus I also tried a new one when installing the drive. I installed a 320 gb Seagate ST3320620A ATA100 into the Secondary Slave position and jumpered it as shown on Seagate's website (no jumpers). I made three partitions, and formatted them as per instructions in XP's Disk Management. They all show as 'healthy' in Windows. The only thing is that my computer has slowed to a crawl, with a re-boot taking about 7 minutes. I checked Dev. Mgr. and saw that the burner was at UDMA 4, but the new drive was at PIO mode, even though 'DMA if available' was selected. I tried Bob's suggestion of changing the settings back and forth and also deleting the secondary IDE channel and rebooting, but nothing works. It remains in PIO mode. I checked all the settings in the bios and they seem correct. Tried alternatives too, but it didn't change anything. On bootup, the bios screen shows all the drives correctly, the drive in question as UDMA 5. I have Windows 98SE on drive 1 on the Primary IDE with Windows XP Home on the second drive, to allow a dual boot. It has worked well until I tried installing this new hard drive. I removed it and installed it in a second machine and it is the Master on the Secondary IDE, with nothing in the slave position. Still in PIO mode. This other machine is also a dual-boot with 98SE on the first HD and XP Pro on the second, both on the Primary IDE.The 3 partitions are in NTFS format and all drives are visible in Dev. Mgr. and all partitions are visible in My Computer.