Rh 7
 

I installed RedHat linux 7, and after I installed it. Nothing starts up. My pc can't find the operating system.

use the boot floppy or redhat cd and install a boot loader to the mbr

Various operating systems tend to think that they are the only operating system on the hard drive or on the system. Make an Emergency bootdisk during installation. Keep this disk handy when you update your system(or any significant system event like repartitioning your hard drive or rebuilding your kernel). Boot using the bootdisk and log in as Root and type lilo on the command line. This repairs the MBR by reinstalling LILO.