If your cpu temp is still at 90-100C then that's your problem and we need to address it and not the video card. While your video card may also have a problem we need to worry about it second as your cpu temperature problem may be the causing the video to act faulty.
If you re-applied the Thermal Paste and your temperatures are still hot then either:
(1) the paste isn't evenly applied or the heatsink is not attached correctly
(2) the heatsink/fan assembly is defective
(3) the motherboard's thermal sensor is defective or
(4) the cpu is defective
I would buy a new heatsink and fan assembly. If that doesn't fix your problem then you would be best off buying a new PC as the cost of replacing your old / obsolete / no longer manufactured hardware will cost almost as much as a new low-budget replacement.
I would help you find a replacement heatsink but we need to know more than it's a Packard Bell with an Intel Processor.