Could be memory, disks, space, cpu or libraries.
Check the easy one - libraries. Hit Ctrl_Alt_F2 if you are in X and log in. start with ldd
ldd /usr/bin/xterm |grep found
anything shown is missing. as for vi, run
yum list vi
rpm -e --force --nodeps (= --middle-finger) vi*.rpm
rpm --rebuilddb (?sp)
then install it.
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