Slow loading web server, even HTML pages (10 seconds to first byte)

Hello, my apache web server 2.x with suphp started loading all the websites slowly (before a few days, it was ok and I made no configuration changes). For example, even a .html page loads about 10 seconds and when the page contains an image, I wait 10 seconds longer for it to appear. So the problem is the first-byte time (TTFB) of my Apache web server.
When I restart it, it shows …

Slow loading web server, even HTML pages (10 seconds to first byte)