after shutting down and restarting lights on and fans are whirring but no indication on monitor at all
I'm still unclear at what point your machine "comes to life".
Do you ever see the initial motherboad / BIOS screen at any stage ?
When see finally see something on the monitor (after 5 minutes), is it a completely delayed boot screen sequence starting with the motherboard / bios, or a fully loaded Win XP desktop - or something in between?
Are there any beeps from within the initial bios load, and if so, how many??
Is there any HDD activity during the period of inactivity (HDD led active - continuous, flashing, or nothing)?
"tis indeed a strange one .....