grub rescue>

I am posting because my issue seems to be a little different from everyone elses. I just installed Ubuntu (the most recent) onto a 640gb sata hitachi drive. THere was no operating system installed so it is not going to be a dual boot. I have not been able to use the computer yet, As the computer starts up i keeps saying file unknow then i get a promt drub rescue>. I have tried googling it everywhere to fix it but i can' seem to find anyone with this problem, most people are running a dual boot. I am not completely understanding all i am ready either. I am very good with computers, but this type of issue illudes me. i have a boot disk and can boot from it it i put it into the computer, but i want to use the full ubuntu system installed to my hard drive. Can someone please help, and try to explain it simply so i can use my new computer.