am unable to open a .log file which is 4MB size.

please post the output of "df -h" or "df -k".

Filesystem size used avail capacity Mounted on
/dev/dsk/c1t0d0s0 24G 9.9G 14G 42% /
/dev/dsk/c1t0d0s7 16G 5.7G 10G 37% /usr
/proc 0K 0K 0K 0% /proc
mnttab 0K 0K 0K 0% /etc/mnttab
fd 0K 0K 0K 0% /dev/fd
/dev/dsk/c1t0d0s4 9.6G 1.5G 8.1G 16% /var
swap 5.9G 168K 5.9G 1% /var/run
/dev/dsk/c1t2d0s0 69G 14G 54G 21% /home2
/dev/dsk/c1t2d0s1 66G 33G 32G 51% /home3
/dev/dsk/c1t0d0s5 9.6G 1.8G 7.8G 19% /tmp
/dev/dsk/c1t0d0s3 19G 4.0G 15G 21% /opt
/dev/dsk/c1t1d0s0 69G 12G 56G 19% /loadbuild
/dev/dsk/c1t1d0s1 66G 59G 6.3G 91% /home1
/dev/dsk/c1t3d0s0 69G 48G 20G 71% /home4
/dev/dsk/c1t3d0s1 66G 30G 35G 47% /home5
/dev/dsk/c1t0d0s6 48G 21G 26G 45% /export/home

Filesystem kbytes used avail capacity Mounted on
/dev/dsk/c1t0d0s0 25206312 10422045 14532204 42% /
/dev/dsk/c1t0d0s7 16646570 5961025 10519080 37% /usr
/proc 0 0 0 0% /proc
mnttab 0 0 0 0% /etc/mnttab
fd 0 0 0 0% /dev/fd
/dev/dsk/c1t0d0s4 10092076 1546678 8444478 16% /var
swap 6153424 168 6153256 1% /var/run
/dev/dsk/c1t2d0s0 72301401 14816895 56761492 21% /home2
/dev/dsk/c1t2d0s1 68883610 34459562 33735212 51% /home3
/dev/dsk/c1t0d0s5 10092076 1849915 8141241 19% /tmp
/dev/dsk/c1t0d0s3 20174761 4159250 15813764 21% /opt
/dev/dsk/c1t1d0s0 72301401 12967873 58610514 19% /loadbuild
/dev/dsk/c1t1d0s1 68883610 61590102 6604672 91% /home1
/dev/dsk/c1t3d0s0 72301401 50260733 21317654 71% /home4
/dev/dsk/c1t3d0s1 68883610 31500221 36694553 47% /home5
/dev/dsk/c1t0d0s6 50432224 22166357 27761545 45% /export/home

Any error/exception u are getting ?

Have u ftp'ed the files from some other place ?

What is the value of:
1. $EDITOR
2. $TERM

Is it taking time to open the file or vi displays that it is unable to open file ?

Probably to check that, you could press ctrl-c after opening the file in vi.

That way, partially file will be displayed in the editor.