My Laptop wont POST and has a Funny looking display. Any ideas?

As the title says. my laptop will not POST, all that happen is i get a full screen of what looks like ‘:’ all the way across filling the screen and in the top left corner i get a horizontal cursor blinking. nothing else will happen. email me if you would like a picture of what the screen looks like.
thanks for any help.

Daniel

dbannon06@btinternet.com