Examples of devices that are not recognized would be helpful in finding cause. Can you give some details?
Also, USB allows for connecting up to 127 devices, but there are limits:
- Every hub is a device, limiting available pool. Your PC has at least several already, by the way.
- You can do max 5 tiers (every hub is another tier, hub is a device to which you can connect another USB device in a daisychain)
- USB has finite bandwidth, be sure you spread devices evenly across the hubs in your PC, some devices use way more than usual peripherals.
- USB supplies finite power to each port, make sure you're using devices with own power or powered hubs as much as possible
- Max cable length is different for each port standard (3.0 has max 5m, 2.0 max 3m)
- It might be a good idea not to mix 3.0 and 2.0 devices on the same chain. Different speeds, available bandwidth and signal attenuation on the long cables all make difference.
If you took all that into account all that's left is to contact the PC manufacturer for assistance in your setup.