Wrong PixelShader version dettected

RwR

Graphics Card: ATI Mobility Radeon HD 2600
OS: Windows Vista Home Basic 32bit

I had a problem with Bioshock, there were a lot of missing textures, almos everything was black. To fix this problem, I used the ATI Mobility Modder, and it worked. The problem is that after I fixed this, it seems that most applications dettect the graphics card as only supporting pixel shader 2.0, but I think it supports pixel shader 4.0, I'm not sure but it says HERE something about Shader Model 4.0 (maybe it's not the same thing, noob alert!). GPU-Z says it is pixel shader 2.0, and most games say it to. Tomb Raider Underworld won't start now, but before the change I could play it. Pro Evolution Soccer 2009 won't let me set the settings to maximum, and before it did.
Did I do something wrong? How Can I fix this?

Thanks.