Nodal analysis independent and dependent voltage source and current source
You forgot the contribution from \$(V_5-V_4)/2k\$ from the supernode. The reduced system is

$$4V_1-V_2-V_3-V_4-V_5=0\\
-3V_1+V_2+3V_3/2+2V_4-V_5/2=4\\
-V_1-V_4/2+5V_5/2=0\\
-V_2+V_3-2V_4=0\\
-V_3+V_4=12$$

which results in

$$V_1=-3.5V\\
V_2=-21.5V\\
V_3=-2.5V\\
V_4=9.5V\\
V_5=0.5V$$