The bottom bracket of my bike was completely stripped to the point that when you push the left side crank arm, the right crank moves and you can see the bottom bracket lock move out the frame. The bike shop tried putting Teflon tape but it's temporary.
It's a 26' xc hard tail. For all I know both sides of the bottom bracket(square tapered) are stripped clean hence the Teflon tape put by the previous owner. Can I fix the problem by changing into a hallow tech cranks because it works like a thread less bb, or should I just buy a thread less square tapered bb?
If I understand your problem correctly it is the drive side that is stripped while the non-drive side (left) is still usable
Depending on the frame (i.e. it's value for you) and the bottom bracket type I see the following solutions:
get yourself a cartridge bottom bracket (with sealed bearings) and glue in the drive-side plug. You will still be able to replace the spindle and the bearings and the pre-load is adjusted with the non-drive side anyway
get this Velo-Orange bottom bracket for stripped shells
have the shell re-threaded for a slightly larger thread, e.g. BSA shells can be re-threaded for Italian threads. You then need new cups or complete (cartridge) bottom bracket
clean the shell and press in another shell with healthy threads, most likely of smaller diameter
get another frame with healthy threads
Please, give some more information on the frame you have, we can then come up with some specific advice.