Are you using windows or linux ?

Id you are using linux, an output from dmesg will be helpfull in wether your computer actually finds the device, and provide more useful information on debugging this.
If you are using windows, I suggest using a Live-CD with a linux distibution, and try to attach the N9 using that booted up. Then, get the dmesg output to post here.

It sounds like a drained battery, so, again, a linuxdistro is helpfull, connect the N9, while powered off (long press power), use flasher to put power on the battery (flasher -i, and wait for the battery to charge)

Other things to try: another USB cable have sometimes caused issues when using a not nokia USB cabler, or USB cable is defect.
If you have a friend, with Linux, also try on his (M/K) computer.