Apache, all connections in waiting

[MassimilianoM]

Hello everyone,
it happens about 5 / 6 times a day by visiting any of our site dedicated server the server freezes.
All services are blocked (ftp, ssh, web, mysql) and then comes back on after 1/2 minutes.

In the advanced statistics of apache I've noticed that in these moments all requests are pending:

Server uptime: 3 days 9 hours 47 minutes 13 seconds
Total accesses: 52935 - Total Traffic: 383.9 MB
CPU Usage: u28.01 s17.82 cu0 cs0 - .0156% CPU load
.18 requests/sec - 1367 B/second - 7.4 kB/request
17 requests currently being processed, 0 idle workers
WWSLWSWLSWWWWWWWWL.WW............................. ..............
.................................................. ..............
.................................................. ..............
.................................................. ..............
Scoreboard Key:
"_" Waiting for Connection, "S" Starting up, "R" Reading Request,
"W" Sending Reply, "K" Keepalive (read), "D" DNS Lookup,
"C" Closing connection, "L" Logging, "G" Gracefully finishing,
"I" Idle cleanup of worker, "." Open slot with no current process

I do not know really what to do.

Thank you