connection problems (D-link dsl-G604T)

Ever since I got my D-Link G604T I have trouble.

When I turn on my computer everything connects with no trouble, but some
times when I leave my computer on for some time and then go and try to
connect I can't get on. Other times I can connect, this has me baffled.

Has anyone got any ideas?

firmware for d-link V1.00B02T02.UK.20041126

I am new to this side of the Internet, before this I had the frog and it
was just p&p with few errors.

Also I can get into the d-link settings pages at any time with no
problems, when I check the settings it comes back saying everything is
connected and the log shows there's no problems.

I have the microsoft firewall switch off and I'm using zone alarm as my
firewall..... the firewall on the d-link is enabled???

please help