Cause of black screen with blinking cursor at start-up

chem15t

Recently, when I power on my system, the monitor is blank with the exception
of a blinking cursor (underscore). I spoke to a service technician a Fry
Electronic and he said the problem was the power supply. I replaced the
power supply and the problem went away but recently has come back. Unlike
the past, where a restart would result in the same blank screen with cursor,
this time the system booted.

Has anyone observed this and if so, what is the cause? Thank you.