Shareaza

Shareaza works great, very fast connection. But after using it for several hours, I no longer have internet access.
(It's still downloading very fast, but zero internet access or mail checking.)

Turning off Shareaza does not help.
Resetting NIC does not help.
Rebooting computer does not help.

The only thing that gives me back internet access is to reboot the router.

Common cases:
1) You have an old/buggy router which is killed by large amount of connections established by typical P2P application like Shareaza.
2) You have a shitty ISP which is blocking a typical P2P application like Shareaza (by policy or by protecting ISP's old/buggy routers).

Router is about 2 years old, ports unblocked for P2P
Keep in mind that the Shareaza connection stays solid, so network access is not being blocked. Only internet access is lost (Even after turning off Shareaza)

On right top there is the downloadmonitor. Move the small red slider to 90%.
Maybe your router is overflooded internaly. So, reset is needed.
Halbwertzeit for Computershardware is 18 month. Which means: Speed doubles up within this time.

Go to some Speedchecksite, check your max connections and adjust
Settings -> Internet-> Downloads-> Maximum Transfers

Most likely your router's firmware is shitty. I had AirLive G.DUO with stock firmware and no matter which P2P app I lauched it killed it.