Wireless Keyboard not working with Dell Studio Desktop.

I have a Dell Studio 540 desktop computer that has been running perfectly since i got it in September 09. I recently upgraded the keyboard and mouse supplied with the computer to a Microsoft Wireless Keyboard and Mouse 6000 v3.0. I plugged it in, installed all the necessary drivers and tried it out. It seemed to work until i noticed that there was a huge lag everytime the HDD light was flashing on the front of the desktop! This made the mouse and keyboard nearly impossible to use and forced me to revert back to the wired keyboard.

I then tried the keyboard on other computers to check if it was the keyboard and mouse, or the pc. The keyboard and mouse worked fine on other computers. 

I assume it is simply due to the way my Dell pc is set up, so was curious if anyone had any ideas on why it's not working and also a way to fix the problem!?

Cheers! EuanTough