Sidekick slide wont charge the light wont shine
There was a known power issue with the Sidekick Slide. Motorola recognized the issue and say the fix was creating extra bumpers to keep the battery from sliding around. You may have one that does not have the extra bumpers and therefore your battery contact is weak.
First, make sure you are using a Motorola brand charger. No other chargers work with Motorola phones, even the cheapy ones from gas stations that claim they do. I would then check to make sure the battery is not swollen. If the battery is swollen, it is bad and needs to be replaced. Next, check to see if the phone has any water damage. Under the battery there is a white dot that turns pink/red if it comes in contact with moisture.
If none of the scenarios above fix your problem, I would suggest doing a warranty exchange.