Solutions
I notice that Dr. Pepper answer is correct. I accidentaly changed the resolution in SRB2 and I saw Screen Out of Range. So that's a possible FAQ to write. Now the solution.
- Find scr_height and scr_width in your config file*. Type here a good resolution**.
* riders.cfg for SRB2 Riders, SRB2CB.cfg for Community Build and config.cfg for any other.
** A good resolution is the one that fits in your screen with good aspect relation. You can use your one(in Screen Properties, Configuration) or this ones:
For standard: 320x320, 600x400, 300x200, 1024x768, 960x800
For widescreen: 1260x768, 1200x800, 1600x900...
And that's in! Look at Changing Default Resolutions topic!