Couple of thoughts.
I can suspend the laptop via the sleep button on the keyboard.
What command is that key press executing?
However, I can't wake the computer again by using either the connected USB mouse or the keyboard
How are you awakening it then? Or are you shutting it off with the power button?
My point is, are you sure it's sleeping and not powering off or hibernating with that key press?
Usually a brief touch of the power button on a sleeping machine will wake it.
Are you sure that the machine is not awakening and it's just the display that you are loosing? There's been problems with nvidea in resuming.
Other than that check the BIOS, try a PS2 device, the power button should wake it.