Even if your pc soundcard is able to output Dolby Atmos, the problem will be to connect Sonos Arc to the pc. Sonos home theater products are made to be connected to a tv via hdmi arc. That means you need a hdmi INPUT that supports arc to connect Sonos Arc to. 
The pc probably will support just a standard hdmi out port. 
The only (and expensive) solution will be a hdmi audioextractor with hdmi arc input support. The hd fury arcana or a feintech vax 04101 or OREI HDA-934 would be ok. 

I know that arc is made for tv. I dont want strictly pc Sonos connection.  I AM using arc as the speaker for tv which have earc enabled ,but my display is from pc. I AM playing games or watching Netflix for example.

Note, there is a difference between ARC/eARC and the Sonos Arc.

The Sonos Arc expects an ARC or eARC signal (different pins on the HDMI connector). I’ve not seen a PC sound card that generates an ARC signal, although I suppose it’s possible. In most cases, this type of return signal is created by the TV set. @Schlumpf suggested some external devices which take a standard HDMI signal, such as most PCs would send out, and converts the audio to an ARC/eARC signal. 

@davegdz 

If you would connect hdmi out from pc to a standard hdmi in on the tv to be used as monitor and Sonos Arc would be connected to tv via an eARC supported hdmi in, you will be able to get Atmos. But therefore the game or movie has to support an Atmos audio track and your pc has to support Atmos.