Black Npc/Mobs

Hey guys i have a laptop that has a 1GB DDR3 Memory and My first day i played minecraft on it my minecraft npc's were Transparent until I installed the Optifine mod. but now its just Black. They seem to be blinking from black to the original Color/texture of the mob/Npc. Please help I really want it to be fixed.

This is my Laptops properties:

Aspire one D270-1865

cpu-intel AtomN2600(1.6 GHz, 1mb L2 cache

Memory-1gb DDR3 Memory

Battery- 3-cell Li-ion battery

Storage- 320 GB HDD