It is possible the laser may be starting to go on it. That system could have had a problem with that when they were fixing it up and not spotted- sometimes "refurbishing" means as little as reconnecting one wire.
There are sites that sell replacement lasers for the PS2- if you are familiar enough with doing this sort of thing you could try replacing it. I'm afraid i can't link you to any sites, however- we have rules in place regarding linking to commercial sites plus some of these tend to deal with items of a quasi-legal nature such as mod chips (which we are against the use of here).