CentOS 5 :: Server Is Very Slow From Ssh In LAN

in my office I've setup a centos server which uses no GUI only the console with apache & mysql for testing purpose, notice that I haven't setup any vhost or any mysql db yet, so the load is 0.00 The strange thing that suddenly one day I tried to login to this "server" from my windows pc (in the next room) via putty , and since that day the "server" is very very slow. What do i mean? when I try to login with SSH it makes 15 seconds or more to ask me about login, and then about password (like it happens in a server with massive load). then when I type the command in the konsole it always delays between letters.

I run top -c and everything is dead (0.00) so there is no load. even If I ping -t localip the machine , after 3-4 pings I get "Request timed out". so I think something is wrong with the local network. If I get connected physicaly in the "server" and start pinging my windows pc it works great, everything is going fast, the konsole is fast (as it should be) and if I ping any other servers it also goes withoute a problem. The I think its not a problem with the "servers" network connection.