GTA SA not opening after installing MMGE 3.0

I think that you should ask on the development thread at GTAForums.

Also remember to read the FAQ on the mod page:

• Partial incompatibility with Windows 8/8.1. Possible fix which works for 50% of users is using modloader: install ENB as usual and move d3d9.dll, enbseries.ini and enblocal.ini to GTASA\modloader\enb\ folder, the rest stays where it is.
• If your game doesn't start, reinstall DX setup from GTASA disk or use this one.

Also I recommend installing SilentPatch, a bug-fixing mod that works as expected (it also removes the requirement of DEP or Data Execution Prevention).