Try again some other USB-Devices!
I had the exact same problem about the constantly 'spinning wheel' on both, SMB/LAN and a USB-Device.
...and in both cases it had to do with a problem accessing the right content...
Regardless of that, it was still possible to see the files (player was able to 'list' the content).
Try to re-format a few of your USB-Storrage-Devices.
The device should be partitioned with 1x 'Primary Partition', which is formatted to FAT32.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux