Problem with Intel 537EP Modem

The problem is that I install the modem, and then, after using it normaly for 1 or 2 days, it just un-installs (I realize it when I start windows and uselessly try to connect). Besides, I have the "common" problem with the "PCI Communication Device (Code 28)" for the modem. ¿How can I solve this? Thanks in advance :)

PD: There's no problem when connecting and being in internet, it works right.

Look in it's properties and see if Windows is controlling the power, and shutting it down when not in use. It may have a problem coming up when you need it.

Seems I can't find that configuration :S. (Btw, I have W98)

Sure you dont have any virus?

No virus. Already scanned with the AntiVirus.