new instance / installation problems

Hi all!

I seem to still have problems with MySQL.
I wanted to create a new instance in order to run some tests of DB
sizes. I want to create a new db, user etc... using teh command line
client

I removed the old instance, and created a new one. Could not login as
root. Simply crashes. Service cannot start. Dont know why.

I uninstalled MySQL, restarted and installed again. Not sure now, but I
could not login as root, the service could start, but dies when I login
as root (which crashes).

Ok, I did the same again, including manually deleting old data etc...
(that has helped before).

The result remains - when I login as root it crashes. Dont know you.
But this time the service remain.

Still, it does not work.

I have had this kind of problems before, also when trying to move a DB
to another computer, which also failed completely, I had to start all
over.

What is wrong? Why can I not start on a new database?

And how to I restore to my old ibdata1 file later on if I want to?

BR
Sonnich