Thanks for the replies!
The dirty lens though had occurred to me, but I dismissed it because the problem was so drastic and so sudden. I think I will disassemble the drive later and clean it anyhow, just in case.
As for the DMA option, no, I am not certain it actually [B][I]IS[/I][/B] in DMA. The “Transfer Mode” box says “DMA if available”, but the current mode indicated “Unavailable” or something to that effect.
I’m at work, so I can’t check atm. When I have more info I’ll post again.