Warning
Before you proceed with the following, answer these questions:
Are you still under warranty?
Does your warranty allow you to open up the machine to check hardware?
Do you know HOW to open up your machine and its components (without doing anything risky for you and for your home/PC/pc components)?
If you are unsure of the answers to these questions, contact your system manufacturer (or the component manufacturer).
WARNING: The steps that follow can void your warranty!!!
Remove the dust from inside your pc, especially from fans and air slits.
Check if the fans are working.
Apply a new layer of thermal past on the cpu.
Clean the slot and the gpu card connector.
Try to improve the fan settings and/or their position inside the case (or get better fans, if they don't suffice).