Can ping, telnet 80, but not ssh or http after few hours

Hi,

Here is is my problem,

I have a dedicated server who stops respond to my web browser or by
ssh after few hours.
I am able to ping it or telnet to port 80, but can't access it using my
web browser.

When I try accessing it via lynx I get the awaiting for response
message.
This problem appears after few hours of activity.

My Linux bix is redhat 7.2

Do you have an idea ?

Thanks a lot for your help.

PS : If I restart it it works well.