My IMac OSX 10.5,8. Has just started throwing me of the Internet after a short time. I get a message you are no longer connected to the Internet . Then if I run the diagnostic it reconnects.

Hello Cathsitaras,

Thanks for using Apple Support Communities.

For more information on this, take a look at:

Mac OS X: Troubleshooting a cable modem, DSL, or LAN Internet connection

http://support.apple.com/kb/TS1317

1. From the Apple menu, choose System Preferences.
2. From the View menu, choose Network
3. Be sure that "Built-in Ethernet" has not the status Inactive listed below the entry in the list of network ports.
4. Make sure Built-in Ethernet is the selected, or primary, network interface: Click the action button (gear icon) below the list of network port and choose "Set Service Order...".Services can be dragged to change order. Services are listed with descending priority.
5. Select a network port in the list of port to configure it.
6. Click Advanced..., then click the TCP/IP tab.
7. Follow your ISP's instructions for setting up this pane. For more information, see Mac OS X: How to Connect to the Internet With Cable or DSL.
8. Click OK when finished.
9. If you have made any changes, click Apply Now.

Best of luck,

Mario