Alright so I just started up San Andreas on it and it did the exact same thing. Intro video etc. all played fine, then when the game itself actually started the screen went completely black.
So I changed some settings on my monitor to do with image size, went back to the game and it was actually there on the screen. Seems to have fixed it.
Put MGS3 back in and tried that. Still fucked up though. The disc is fine. I will try it in my PS2 later. If it's fucked up in that then I know it's a problem with the disc. If not then I'll try my PS3 on a TV rather than a monitor and try to determine if it's a screen resolution problem. Can't think why it would matter though. Really strange.
EDIT: FUCK ME. I feel semi-retarded now, however, why I thought it wasn't working is understandable since I'm NOT JAPANESE.
I dunno how many of you are aware but you know how we're all used to pressing X as the "start" or "continue" button on menu screens to go forward to the next screen? Well, the Japanese use the O button to do this. On some Japanese games, Gran Turismo games prior to the third one were like this, except Sony were clever and made it so you could press X or O to continue, and Square or Triangle to go back.
No such joy on MGS3 (or at least my copy, and I checked the SLES code, it's a normal UK copy). Konami seem to have made it so you can ONLY press O to go forward, not X. Of course I've been pressing X all the time like a normal UK gamer which was going backwards a screen rather than forward. Oh well. At least I know how the fuck to work the game now... I'm glad I managed to figure it out for myself actually
I swear MGS2 was never like this.
So, how long can I expect completing MGS3 to take me? If I recall, they're fairly long games aren't they?