Hey rupesh11iri,
If I understand correctly, the screen is flickering and you were able to reset the SMC and NVRAM and that solved the issue in the past but is not fixing it this time. It could be that there is interference from other sources causing this to happen.
You may also be experiencing interference from a nearby power line, a fluorescent light, a radio, a microwave oven, another computer, or another electrical device. Try relocating nearby electrical devices or moving your Mac and display.​
If none of these solutions work: If you have an Apple display and can’t correct the problem, contact an Apple Authorized Service Provider for more help. Don’t attempt to repair the display yourself, because any damage you may cause is not covered under your warranty.​
macOS Sierra: If your display doesn’t look right
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Thank you for using Apple Support Communities. Have a good one.