Linux doesnt boot after showing finding modules OK status
 

When I start redhat linux7.0 on a intel p4 1GHz system with 512 MB RAM (which i upgraded recently) also had a network card. It stops after reaching the step finding modules which has the status OK(after this no message at all ).If i try again by restarting 3-4 times linux will load correctly.but the problem remains unsolved since it appears again if i restart.Please give me a solution if anyone knows.thanks in advance