According to the eMate 300 owner's manual, users should refrain from using third party power adapters, as they are known to cause damage to the unit's power supply. As a result, one should only use the authentic Newton 9 watt adapter that originally came with the unit (the same concept applies with Quicktake 200 owners. If a user wishes to connect their QT to a wall outlet, as opposed to constantly relying on batteries, they can only use the AC adapter that originally came with the QT. Ironically enough, the QT AC adapter was an option, but that's another story for another thread).
Unfortunately, it would appear that you've "innocently" fried your eMate's power supply by using a generic power adapter, hence the abnormal phenomenon with your indicator light, and the fact that it refuses to power up.
Btw, did your eMate come with the original battery pack, or a rebuilt one? Mine came with the original, and it still holds a decent charge, considering it's now 14 years old.