Ping works internitently

I have an XP PC on my network which has recently started disappearing!
Rebooting that PC sometimes restores the connection but more often not.
However that PC can always see the Internet thru' the same connection (to
the router)!

I have just discovered that I can PING the PC from another on the network
but only get some replies:-

Pinging 192.168.0.4 with 32 bytes of data:

Request timed out.
Reply from 192.168.0.4: bytes=32 time10ms TTL=128
Reply from 192.168.0.4: bytes=32 time10ms TTL=128
Reply from 192.168.0.4: bytes=32 time=14ms TTL=128

Ping statistics for 192.168.0.4:
Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 14ms, Average = 3ms


Is there any obvious cause for this, bearing in mind the it can still see
the Internet O.K.?

Thanks

Nigel