Comp won't start

Nothing happends when i press the start button. It seems during the night there was a power shortage (computer was on) and now it won't repsond at all. there is a green light on the lower right corner of the motherboard blinking continously. If i recall correctly that light should be a steady one, not blinking. Hullett Packard  4550, windows 98.  I wont start.  It seems to start when I press the power button but it doesn't send the signal to the monitor.  the monitor is fine.  I tried the pc with another monitor and it does the same thing.  when I press the power button to turn it off, I have to keep pressing the button for a while until it goes off. Thank you very much. Wont start likights blink and monitor wont start nor will cd slot open "HP pavilion 505 n"