Can't seem to NMAP

I cant seem to NMAP localhost or even my IP address, actually i cant seem to nmap anyone. Response I get is

"Note: Host seems down. If it is really up, but blocking our ping probes, try -P0
Nmap run completed -- 1 IP address (0 hosts up) scanned in 12.264 seconds"

i can still ping anyone and can also be pinged
What does it mean if you cant NMAP yourself or anyone else for that matter?

On RH I could specify my own IP as nameserver then just put in GW address of a router connecting to the net and i could connect to the net and resolve locally. I cant seem to do this on SUSE. If i specify myself as nameserver i cant connect to anything, not even anything on my own pc.

Could there be link between the first query and this one?

have you set you network mask correctly?

255.255.255.0 is what most use.

Yep everything is set up correctly, but for some reason i cant seem to nmap.

Do you know what this could mean? ( Not being able to Nmap)