is second life down I cannot log in

[tay Royce]

keeps saying host name cannot be resolved

[Lindal Kidd]

That's not a problem with SL being down.  First, try rebooting your internet modem or router.  If you still can't log in, try using the free Google public DNS servers.  See this link for instructions on how to do that: https://developers.google.com/speed/public-dns/docs/using

[Nalates Urriah]

Your aren't giving us much to go on. When asking a tech question include information about your computer and viewer. Mac's have this problem more often than Windows machines. 

The easy place to get the info is from the viewer's HELP->ABOUT... You can get to it after the viewer is open and before or after you login.

On Windows, open a command window (app name CMD - Type cmd into the Cortina or Start field).

Type nslookup secondlife.com and press Enter. If that fails to find SL, you have a computer problem. It can be fixed. Part of the info is on the page Lindal Kidd gave you. There is more info about DNS and how to change it and remain connected to your ISP's DNS, which is often needed if you report Internet problems online. See: http://blog.nalates.net/2011/10/26/troubleshoot-your-sl-connection/

[Innula Zenovka]

In general, if you have problems logging in and are wondering if it's you or if it's the grid, try checking SL's Grid Status Reports.   

There is usually a bit of a delay between a problem developing and it being posted in the Grid Status reports, so it's not an infalible source of information, but it the problem is of any seriousness and lasts for more than half an hour or so, it should be there.