Disk Problems in Linux

i have recently installed Red Hat linux 7.1 on my Celeron 300 machine with 128mb RAM. due to a system lockup i had to restart my system manually. i powered off and then back on. Now it says that some errors are on root filesystem. Run fsck manually (without the -a). when i run fsck it says parallelizing fsck. What do i do? i can’t start linux