If the error stops, your overclock was unstable. Permanently reduce your core clock by 50-100 MHz for long-term stability.
While "errgfxd3dshader1" is likely a variation of common Direct3D initialization errors (like ERR_GFX_D3D_INIT
Check for Game Updates:
If you can’t reach the menu before crashing, edit settings.xml manually (find <Tessellation value="1" /> and change to 0).