Question Squares on screen and crashing

[Dthomas1997]

I custom built my PC a couple years ago, now when I turn it on sometimes white sqaures will appear In diagonal patterns on the screen. After this it will usually crash and I have also notice the PCs performance has dropped and even crashes occasionally during gaming. I'm guessing this is a problem with the graphics card but what can I do to solve it? I have a Radeon rx480 graphics card. (I do have a pic of the screen when crashing but unsure how to upload)

 

[PC Tailor]

• Please post your entire system spec including PSU make and model.
• Upload your picture onto imgur.com and post the link here.

 

[Dthomas1997]

• Please post your entire system spec including PSU make and model.
• Upload your picture onto imgur.com and post the link here.

Sea sonic G series 550W (80 plus gold) PSU / Radeon RX 480 4gb / B250M-DS3H Motherboard / Intel core i5 / 8gb ram

 

[Dthomas1997]

Sea sonic G series 550W (80 plus gold) PSU / Radeon RX 480 4gb / B250M-DS3H Motherboard / Intel core i5 / 8gb ram

https://imgur.com/a/mLY3IXJ

View: https://imgur.com/a/mLY3IXJ