The amber light flashes once, any devices such as headphones with LEDs flash once too and the network cable light is always on. Add-ons are as follows new graphics card and extra hard drives; both portable - all these have caused no problem for at least a year.
Edit: Also - I use Vista Home Premium, I don't know how relevant this is but I thought it may help.
Edit: Also - I use Vista Home Premium, I don't know how relevant this is but I thought it may help.