P.O.S.T is the black screen with white letters that usuall show on first boot and tells what major hardware is installed and includes on what key to use to enter BIOS or setup.
P.O.S.T means 'Power-on self-test' Power-on self-test - Wikipedia, the free encyclopedia
If you see the POST page then you should be able to enter the BIOS or setup by toggleing a certain key during the post. F1 or DEL or F2 or F10, F11, F12. your computer manual will tell you which key to use.
If the POST is too fast to read you can use the pause/break key to pause it when it first shows up on screen.
The blinking curser and asking for CD leads me to believe that you have a hardware issue with your harddrive. By going into the bios or reading the POST you can tell if the harddrive is actually being read.
Also what is the make and model of your computer?