I had a bunch of flourescent lights with the tubes went bad in my garage.
Some are 48" long ones and some are the U shaped tubes. Since I had seven
sets of lights I have been lazy and waited till now to replace them after
about six of the tubes burned out and 2 that are immiment (doing the
flickering thing and if I turn it off and back on again it will come up).

Now I bought 10 new tubes and replaced them. But out of eight tubes only
two came on the other six remain dead. It is a little tricky to get them in
and I had to push and twist them into place. I tried removing them and
reseating them again, no luck.

I must be doing something wrong? Are these tubes polarized? or can it
either end go in either socket? Even the U shaped tubes do not lit up and
there were working fine (flickering) before I installed the new ones. I was
pretty careful when I removed them so I don't think it is likely that I
damaged the sockets when I removed the old tubes.

Any idea?

Thanks in advance.

MC