Major problelm, please help?

[DougY]

Im usually able to fix my computer problems, but Im stuck here and need some help.
I have an iMac, Intel Core 2 duo, 3.06 Gig, 12 Gig Memory, and a 27" monitor. Im using Lion OS, and it is fully updated to the most current version.
Im using a Belkin N1 Wireless Router.
This machine is my first Apple Computer, and has been running flawlessly since I bought it new almost two years ago.
However, for the past week, everytime I start using the computer, within an hour or so, I lose internet connection, and Im assuming that because I get that funky icon on Mail Inbox, and my browser will not connect to any site. The lights on my Router are all on, and it appears to be functioning correctly.
When I click on the Mail Inbox icon, it brings up a screen that says bring all accounts online. However, when I click ok, nothing happens.
If I shut down the computer, and reboot, everything works fine for awhile, and then the same thing happens again.
I really hope someone out there can ID the problem I'm having and help me.
Thanks

 

[derbothaus]

Can you ping the router when this happens? Network Utility, ping 168.192.1.1 or appropriate .1 for your IP range.
Or in a Terminal shell:
ping -c4 192.168.1.1 (or whatever number your router is)

If you can ping it successfully reboot the router. If problem returns reboot the router but do not shut down your Mac. If you are able to get online now I would try setting yourself a static IP as your router's DHCP may be screwy.