dimension 5150 blinking amber light

my dimension 5150 gets a blinking amber light when power is applied - will not boot, just blinking power light, then will boot for no apparent reason and after many times to press start button. it does have a green light on mother board when power button is first depressed and from thereafter when power, via the power cable, is reapplied (disconnected and reconnected). i followed procedures in dell troubleshoot sequence but i quit when it started talking about taking out cards, etc. on system restart it turns back on fine - solid green light on start button; it is cold starts that are the problem. i see this problem as an faq common thread among dell users - some say is bios battery, some say is power supply internal problem. ok, so what is it and how do i test for it? this is the first computer in my life i ever had a problem with in less than 2 years of ownership - like one and one-half years ownership - so i am not too pleased. i have a couple dimension 4100s children use that i have never had a problem with as well as a couple older compaqs and 2 alaska computers from mexico that keep on working so the new dell problem is very irritating. (and all the early dos and 3.1 computers i had never pooped until i finally threw them away.) the real odd thing - i came in today to start it up and amber light came on, when i depressed the start button, and it began blinking. pushing the button would do nothing from then on. tried different (known to work) power cords and wall outlets and same result; took off front panel to see if button was stuck - not the problem. the real odd thing is that when i disconnect and reconnect the power cord, after waiting for green light on mother board to discharge, the computer automatically returns to blinking yellow button status (and motherboard green light automatically comes back on). i find this odd because my first thought would be that the system would be in a completely inactive, i.e. dead off, state when the power cord was reattached instead of returning directly to the blinking yellow start button and solid green motherboard light. so the fact that disconnecting the power then reconnecting the power does not 'zero' out the whole thing must be a clue . . . and it restarts by itself fine. ok, sherlocks, what is going on? thanks in advance.