You should be able to boot from the CD drive instead, but you will need to alter the bootup sequence in the bios. You can get into the bios by pressing the 'del' or sometimes the 'F2' key just after you start the computer. (if you have the manual this might be a good time to refer to it, if not then try downloading a PDF version from the manufacturers web site)

I expect someone can give you more specific instructions if you can say what the make of the laptop is and the bios make and version (this will most likely be the first thing to apear on the screen when you power up the machine).