Internet gradually slows down

I am using a desktop computer with Windows 7. I am connected to the internet via a Netgear wireless router, and recently I have been experiencing a problem where my internet speed gradually slows down and ultimately I am unable to load webpages/internet content through any browser/other software (eg skype calls, dropbox). 

When I initially boot the computer, internet speeds are fine, but the longer I use it the slower my connection gets.

I have many other devices on this network that have no problem with internet speeds - a Mac laptop, a Playstation 3, a 3DS, a Playstation Vita, an iPhone, etc. this problem is isolated to my Windows PC. I assume it is a software or configuration issue as my signal strength is strong (literally three metres away from the router, my computer is relatively new (less than a year), and the problem seems to 'fix' itself when I reboot my computer each time, until the connection starts to slow down again.

What might be the cause of this problem? I'm happy to respond with configuration info on my computer and router if you let me know what is relevant to post.