Downloaded 2.73 & 2.73a - Seems very slow

So just downloaded 2.73 version off blender.org and seems very lagging in regards to basic functionality such as scrolling to zoom and simple things like extruding the default seem to be very laggy (technical term :P). The previous version of Blender I had worked well. I tried to re-install that but the problem then appeared in that as well.

Also just tried the 2.73a version and i’m seeing the same results.

Was just wondering if anybody had any idea of why it’s doing this when it was working perfectly before

Here are my system specs just in case, but never had a problem before.

Intel Core i5-2500 CPU @ 3.30GHz
Ram: 8GB
Windows 7 64bit
AMD Radeon HD 5450

Thanks in advance, James