Gregory Lehr-Milberg.....If you are getting a ISP error exactly what is it ...or are you just calling it an error ?
If your connection is lost after checking your E mail....its possible you have the Box ticked that says close connection after receipt of Email ( or something like that ) You say you lose connection while surfin .......is this time related or just a random thing ?
You also mention that you loose connection when your pc is sleeping......It's possible that if your ISP sees inactivity it will disconnect you. I would check all your settings , your modem and if necessary run your issue past your ISP.
The other thing is if you let us in on what your o/s is and the type of modem you have ..it may be easier to assist you.
Hope this helps you .
dl65