Since we do not know for a fact that the phone was stolen, let's stay away from that topic for now until the OP finds otherwise (and you can do that easily by calling AT&T with the IMEI number from the sticker under the battery). Plus since we do not allow discussion of stolen or illegal, again we should stay away from that topic, otherwise I will have to close this thread and I do not want to do that.
So assuming the phone is not stolen, and just that the previous owner either lost or kept the cables and charger. Any micro USB cable (like from a blackberry) and ac wall to USB adapter should work. I use my friends blackberry adapter and USB cable at work and it works fine. If the phone is dead, usually a computer USB port will not be enough and you need a wall charger. And even if it is bricked, it should still charge with a wall charger, which you will need to do so you can try and flash it back to life.
Now once the phone is charged, and you can tell by pressing the up volume button when charging and it will show the battery level, if it boots up and has the old user's info it will be locked. So you should do a factory reset to unlock it and get the old user's stuff off of it; when you boot it up, boot into recovery mode. Look here
[How To] Enter Recovery Mode on the Motorola Atrix for that and the menu options.
If the phone will not boot up, it may be bricked and you need to reflash the firmware to get it running again. Use the 1.26 SBF here
[How To] Enter Recovery Mode on the Motorola Atrix to return tothe original stock. Then when you have everything up and running, perform the updates to get back up to the most current version. If that does not work and the phone is bricked or is stolen, you need to contact eBay and paypal. Well good luck and let us know how it turns out.
