Hello messi1991 and welcome to TSF,

Check your power settings to make sure you are running at full performance when plugged in.

It sounds like your system is throttling back on power, when it should be the opposite.

 

I've checked and it's in high performance mode when on a/c power and on battery.
I've also checked the Catalyst Control Center and the GPU is set for max (3D application) performance on both battery and power.

 

There may be an issue with your PSU (charger). Dell laptops have a little oddity, when the computer detects a non-dell psu, it will throttle back the CPU. This feature has been integrated into dell laptops for quite some time. I have seen some Dell laptops do this when plugged into the factory PSU.

Run the Dell Diagnostics at start up. The program should tell you if there is an issue with your power supply.

 

I ran the Dell Diagnostics as you said, but no luck. It didn't detect any problems with my charger.

 

Okay,

Check your Catalyst Control Center settings...

Do you remember installing any software or receiving any updates about the time your issue started occurring?

 

No in fact I hadn't used the laptop for about two weeks before this started.

Also I've searched around and found that this is probably a dust issue leading to heating of the CPU. So I'll clean the air filters and let you know hoe it goes. Thanks for all the help gavin.

 

It could be. The reason I din't jump right to that is the issue with connecting the PSU. Regular cleanings of your laptop are necessary for proper performance and longevity.