Sometimes packet filtering firewalls block standard ICMP ping requests.

In that case, use TCP ACK and TCP Syn methods to scan remote hosts.

sudo nmap -PS 192.168.1.69

result:

Starting Nmap 6.40 ( http://nmap.org ) at 2016-07-08 01:22 BST
Nmap scan report for peter-laptop-1 (192.168.1.69)
Host is up (0.0000060s latency).
Not shown: 997 closed ports
PORT    STATE SERVICE
80/tcp  open  http
139/tcp open  netbios-ssn
445/tcp open  microsoft-ds
 
Nmap done: 1 IP address (1 host up) scanned in 2.44 seconds