Hi, I am using my Sapphire HD4870 from last 1 year with no problem but now from last few days I'm facing heating problem with my graphic card. Systems starts well, boot well but when welcome screen appears display goes blank and system restarts. But if I try to run my PC without graphic card, it works well.
Sounds like either the fan is dieing or you have caked up dust. Clean out the computer and GPU with a can of compressed air. After that monitor your temps with GPU-z or MSI afterburner and ensure your fan is working like i should be.