Would someone tell me what a generic setting is to connect to the internet using openwrt Linksys wrt1900ACS v2 firmware or any router... I can't connect, windows 10 wizard says DNS Name not working... I've used 1.1.1.1. and .10.0.1 for DNS names. I setup LAN for static, dhcp server enabled. what I can NOT see is an ip address from my service provider, comcast. I can't see or find where this is enabled or set. I've just killed my internet connection, can't revert back to original Linksys firmware, the openwrt says "file not compatible". I don't get it.
You don't really specify anything about your internet connection to go by (and no, there is nothing generic about this).
But by Comcast I assume you're talking about internet via TV cable, if that is the case - reset your router to (OpenWrt) defaults ("firstboot"), to make sure you revert to plain DHCP without any (potentially wrong) customizations, switch off router and cable modem(!) for about 15 minutes (to allow your ISP's DHCP lease to expire) before switching modem and ~5 minutes later the router on again.
This might not necessarily help, but it has a good chance to do (cable ISPs lock on the router's MAC address and refuse to serve another MAC before they're convinced that the original station is gone) - and the beauty of it, you can't break anything before debugging further.
Default DNS not found. When I plug in my old DLink and reset my modem it connects. But I've reset the Linksys wrt1900ACS with openWRT and it fails to connect. I go to the LAN page its set to Static address, netmask is set, IPv4 gateway blank, IPv4 broadcast blank. I like to use custom DNS 1.1.1.1 & 1.0.0.1 but I set those to blank too. Per your response, I should just connect using default settings? Any ideas here, do I need a DNS server address?
Comcast, at least where I am, can be "sticky" with its DHCP. You might need to wait a while until your old lease ages enough without any activity. You might call Comcast support, but my experience has been that their hold times and the time until you get someone that has enough knowledge and authority to do something takes longer that waiting it out. Perhaps tonight, before you go to sleep, follow @slh advice on a reset of your OpenWRT config, unplug your old router, plug in the new, and reset the modem.
Edit, Yes, for starters "take" whatever is assigned to you through DHCP. Once that is working, it is straightforward to configure things like your own choice of DNS servers.
This is common with cable modems. It prevents multiple devices (MACs) from being connected connected to its Ethernet interface (i.e. trying to obtain multiple Public IP addresses).