Hmm. Don't know. If the PS2 is spending all its time trying to read the disc, then it may not run through its startup.
The original problem (first post) I would guess to be the lens, else the software of something else is fried. If even the browser menu won't come up, then I'd say you have a problem with the built in software. I don't know how the built-in software works on PS2, whether it's some sort of hard drive or actual ROM (memory chip), but if the software gets corrupted, then the whole device will cease to function correctly. I work with mobile phones at the moment and I see quite a few problems from software malfunctions.
If it comes up with the browser menu but won't read discs (or specifically won't read the GT4 disc) then I'd say the laser is out of alignment.
If it won't come up at all, I'd say you have a software problem. That's all I can think of. Maybe do a google search for troubleshooting...