well this may help with your question found this on another site.
Just to clear things up: Meanwhile I found the solution: The Intel HD4600 isn't the issue, for all I know it can output 4K just fine via HDMi (but not via DVI). However the Dell U2713HM will only accept resolutions of up to 1080p via HDMi, for larger resolutions like the native 2560 x 1440 you'll need to use DVI or DisplayPort. This is of course a problem with the output specifications of my mini ITX Board, which is why I went for a small dedicated Geforce GPU which gives me 2560 x 1440 via DVI just fine. It's kind of a sad state though - my Gigabyte board has 2 HDMI and 1 DVI out and all of them are useless - at least with this very Dell display. And don't bother with Pre-Haswell boards either, I was shocked to learn that larger than 1080p is quite a new thing for onboard GPUs.
THat said be sure to double check your display and mainboard specifications. Or if it's too late already, buy a cheap dedicated GPU.
prices for gtx 770
http://pcpartpicker.com/part/evga-video-card-02gp42776kr
price for a r9 290
http://pcpartpicker.com/part/asus-video-card-r9290dc2oc4gd5
still comes with free games
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121842&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=