Replaced battery and HDD, iPod won't turn on

The HDD on my 120 GB iPod Classic (6th Gen) recently went bad, so I bought a Tarkan iFlash (ZIF to CF to SD) adapter and a 128 GB SD card off his list of recommended cards. At the suggestion of many, I also bought a replacement battery from ipodbatterydepot.com. I've installed both, but things are not working as expected.

When I turn HOLD off, nothing happens. When I connect the iPod to my computer (Windows 7) with HOLD on, nothing happens. When I switch HOLD off, the screen blinks on and off (on for a second, off for a second, repeat) and shows the Apple logo when on. Holding Center+Menu slows the blink rate down to about 3 seconds, but does nothing else. Holding Center+Play does nothing.

I left it connected for 24 hours hoping that the battery just needed to charge, but it still behaves like it did yesterday.

I tried re-seating all the ribbon cables and everything seems fine. I tried reformatting the SD card to FAT32 as others have suggested, but the only formatting options on my computer are exFAT and NTFS, so I left it as exFAT.