This is typical for the following hardware issues.
1. An overtaxed power supply unit (PSU.) The P4 1.7 Socket 423's I have at the office run on 400 and 450 Watt PSUs. Very stable.
2. We had a batch of motherboards that did just that. They had the bad motherboard capacitor issue you can see at http://www.badcaps.net/ident/ Eventually the boards failed to boot at all. Very annoying issue that can extend to other boards and power supplies.
3. If you have to hit the reset to just get the OS to start loading, it's not an OS issue.
Bob
i have P4 1.7/256, MB Gigabyte (8ID2003) and 256 of RAM and installing winXP-pro
i faced 2 problems NOW..
1- everytime i try to power on my PC it didn' open from firstime.. i must push reset button several times till it open..WHY??
2- If my PC opend after the previous problem i face the second one that when i log to the Windows (XP pro.) it worked somtime and in the mid. of my work, suddenly it restart himself to face the first problem that i talked about above..again..WHY??

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic