Will this PC be able to run Diablo3 and Skyrim without any probs ?

OS Windows 7 Home Premium 64-bit
CPU Intel Core i7 processor 2600 - 3,4 GHz
RAM 12 GB DDR3
HDD 2000 GB SATA 3G - 7200
GFX NVIDIA GeForce GTX 550Ti / 1GB dedicated
SOUND High Definition Audio 7.1
WiFi 802.11 b/g/n
LAN Card 10/100/1000
Optical DVD
Ports 9 x USB, 1 x HDMI
Card Reader 15-in-1

should be np.

i have somewhat worse CPU and about same quality GFX and i have no problem to run skyrim. running it on ultra or very high with graphic mods

Check under www.systemrequirementslab.com. If anything, you should be more concerned about running skyrim since I imagine that's more graphically intensive than D3.

i have way worse PC and both of these games runs fine in 1920x1200,medium quality textures

That it is. My back-up video card (getting my nice one tomorrow!) can run D3 just fine, but can't run Skyrim. They are set to run in equivalent settings.