Did you recently open the ps2/modify it?
Found this which may help (and will void your warrenty):
When you take the top cover off of the PS2, you can see where the Reset/Eject ribbon cable plugs into the system itself. Right next to and slightly below here are three wires with three tiny color-coded plug-ins attached. They are just pressed into place and have a tendency to work themselves out over time. And depending on which one came undone, the disc tray will either always want to stay closed or always want to stay open. Either way, the operation of the disc tray will be erratic and problematic.
So it's a matter of using a pair of needle-nosed pliers to grasp and make sure that all three of these tiny plug-ins are fully inserted into the slots where they belong. Sometimes it's even necessary to very slightly lift the PS2 out of the bottom half of it's shell to gain better access to them. After they're all clearly in place, then it's a good idea to use the same needle-nosed pliers to make sure that the ribbon cable did not slightly pull out of place from where it is plugged in as well, or the Reset/Eject buttons will not work.
After all this, you can put the PS2 back together and voila...you should be good to go!