RPi not connecting to network

[bharathyes]

Hi,
I have been using my RPI B+ as a torrent box for a couple of months now and everything seems to be working fine. But suddenly it became inaccessible in the network even though all lights( power, activity, two ethernet ) are turned ON as usual. But I can't access it through puTTy, terminal, VNC, transmission's web UI. It says that the host is down, even though the Pi seems to be working normally.
But there doesn't seem to be any activity on the ethernet except for an occasional blink.
Then I checked my router and say that the Pi isn't listed on the DNS LAN Host list while all my other devices are listed there.
Also I tried pinging it and got the response :

PING 192.168.1.17 (192.168.1.17): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2
Request timeout for icmp_seq 3
ping: sendto: No route to host
Request timeout for icmp_seq 4
ping: sendto: Host is down
Request timeout for icmp_seq 5
ping: sendto: Host is down

Please help me figure this out guys.

P.S.: I don't have a display connected to it and only use VNC till now.

[B.Goode]

Is it possible that your router has assigned an IP address to your RPi for a finite time which has now expired? Have you tried rebooting either or both the RPi and router?

[DougieLawson]

Is this wired or wireless?
Is this DHCP or static IP addressing?

If wired, do you have green lights on both ends of the cable?