I can hear my Mac boot up and see the circular thinking wheel and then it goes to a blue screen what is the problem?

Hi, I just recently returned home from a vacation and was gone a week. I used my Mac desk top and thought I had turned it off. In the morning a message came on talking about word not being shut down properly and I could loose any unsaved material. I cancelled it out and then it immediately went to a blue screen. I tried all the things I could think of, unplugged the mac etc, and it always goes back to a blue screen. I did call someone who suggested I press the control button when starting my computer back up and I got a small box with a hard drive picture and an arrow below it. I clicked on the arrow and it went to a blue screen again. I have also unplugged all connections to the Mac and started it back up with only the power button on and it went to a blue screen. I started it up and put in snow leopard as suggested and now I can not eject the CD. My computer is probably five yeas old, I have never had any problems. I just added some rams I believe back in early December and it worked great.