Windows slow on brand new machine

Hi everyone,

I just got a new ASUS ultrabook (this week) that should be quite fast given the config (see config at the bottom). It is very fast indeed for internet browsing, video games etc, except all windows related tasks. Main examples:

- Opening a new folder can take 10 to 20 seconds
- Opening windows settings takes approx 15 seconds
- Opening a picture (!) takes approx 15 seconds and can make the computer freeze for a while

Something else I noticed: when I want to check windows updates, it doesn't seem to find any, but it doesn't tell me this; instead it just keeps looking for updates without ever ending.

Also as I said everything not windows related is very fast, I can open 30 tabs on chrome without any problem etc.

My suspects :
- A virus (after a week only??)
- Some of the stuff ASUS installs by default on their machines

Any help appreciated :)

My config:

Brand: ASUS Zenbook UX302LG
OS: Windows 8 Pro
Processor: Intel® Core™ i7 4500U Processor
Memory: DDR3L 1600 MHz SDRAM, 8 G
Graphic: NVIDIA® GeForce® GT 730M 2GB DDR3 VRAM
Storage: 750GB HDD With 16G SSD
Antivirus: McAfee (installed by default, will change it asap)