Your Gamer 2 Amp turns on whenever an audio signal is present on the input. The amp can have trouble tuning on if the output of the source (computer sound card, etc.) has been turned down. This can happen easily if you use amplified speakers - if you turn the sound card's volume control down - and then increase the volume at the amplified speaker - the resulting sound is the same; even though the signal has been lowered. The problem is that the output from the sound card isn't sufficient to turn on the Gamer 2 Amp.
Try turning down the external speaker volume, then bump up the sound card volume. You'll probably need to adjust the other inputs individually (Wave, Mic, CD, etc) so that none is too loud or soft. Once the input values have been set, gradually increase the output of the sound card in the control panel application etc. while decreasing the volume on the amplified speaker to maintain a comfortable level. Eventually, you'll find the correct volume level on the sound card output that will wake up the Gamer 2 Amp.
If you're still having trouble, review the manual, here
. I hope this helps & good luck!