Luckily, this is an easy problem to fix. The GTX 750 has only 4 screws holding the heat sink and fan assembly. We removed the 4 screws which have springs on them to provide tension on the ASIC and the heat sink surface.
We then cleaned the ASIC surface and we also cleared the heat sink surface. We used toilet paper and a small amount of alcohol to remove as much of the residue of the OEM thermal pad as possible.
We then applied a small dot (half of a bb size) of Arctic MX-4 on the ASIC center. There is no need to spread it, natural thermal spreading will do the work for you. The springs on the cooler screws apply a moderate amount of tension.
We then reattached the cooling assembly and installed the card. The screws attack easily into the assemble screw holes. We then tightened the screws and made sure the fan was not fouled. The machine powered up and the fan was working fine.
After Windows was finished booting we loaded the Furmark tool and ran the stress test. Immediately the performance was markedly better. With the throttling the GTX 750 barely managed 7fps. After the MX-4 the card achieved 23fps and the card never got over 63°C so the card is now thermally stable.
Thermal pads do not have a very good service life. They also perform poorly. We used MX-4 which is expensive but it performs well and it has an 8 year warranty for service life. Video cards are expensive so we want them to last a very long time. Refurbished, the Gigabyte GTX 750 can now play games for many years to come.
We have used MX-4 for a long time in out studio and it has delivered outstanding results and we recommend it for any repairs.
WE STILL HAVE A GT 630 AVAILABLE
Had we failed to repair the GTX 750, we do have an old Asus GT 630 available which can make do pending a new video card. The GT 630 is Fermi which is now out of support but it has 2 compute units so it can play some older games just fine. With 2048MB VRAM it it also best with 64-bit Windows.