I hav RH Linux 5 on my desktop. when i start linux while booing it stuck at "STARTING NFS QUOTA"

Most likely trying to connect to an offline NFS system. If you can try and do a live boot and edit your /etc/fstab file and remove any NFS devices in list. Or power on NFS device/machine prior to powering on desktop.

pc is standalone not in any network..i m new to linux...can u tell me step by step. Will b thnkfull to u.

ok - first try going into single user mode

Hit enter - When you get to grub screen (Where it countsdown to select RHEL 5 automatically)

Select Red Hat Enterprise Linux with the version of the kernel that you wish to boot and type a to append the line.

Go to the end of the line and type single as a separate word (press the Spacebar and then type single). Press Enter to exit edit mode

type in the root password

next type :

If there is a line that has an ip in it delete it by using 'j' key or down arrow to that line and typing 'dd' --
If there is no line with an ip than there is another issue.

--If there is then after deleting line save file by typing ':wq!'

Finally to get out of single user mode type 'init 5'