This isn't as simple as the question puts it. By "old system" I mean old and broken system that I sent into Sony that got replaced by a 120GB Playstation 3 system. From gradually going to my friends houses I have succesfully got my account onto 5 other systems other than my own. On MY system I can download and purchase stuff from the Play Station Store. But for some reason now, when I had deactivated my account of one of my friend's system. It won't let him reactivate it. Please help. I need to get my account off of that old system.
The only way to do that is to call Sony on the phone 800-345-SONY, and give them the serial number of the old PS3. If you sent it in for replacement, Sony will have a record of that, and they will deactivate the PS3 from your PSN account for you. If you don't know the serial number, then the only other thing you can do is ask Sony to reset all of the PS3 activations on the account. Sony's policy is to do this only one time, ever, for each PSN account; so it should be a last resort. By the way, you do know that you are not allowed to share Playstation Store purchases with your friends at all, right? If you do download something to your friend's PS3 while you are visiting, you should deactivate the PS3 from your account before you leave. Otherwise you are in violation of the license terms. The whole point of the 5 PS3 activation limit is to prevent people from sharing Playstation Store purchases with their friends. You should be clear on that before you call anyone at Sony.