: Found 2 computers doing this recently, one was on a farm and the electric fence passed over their ISDN line annd every time it pulsed it reset the computer, and the other one reset itself everytime the shower was switched on. This one also had ISDN. Check power supply for heavy pulsed interference and also the phone line.
: Check the power by either looking for interference causes (fridge etc) or by using Uninteruptable power supply. Check phone by unplugging line from modem and/or listening for interference