System woes after uninstalling

Hey guys

I currently have three machines (all Acer/Intel chipsets) running vista premium. Have never had any issues, except removing the bloatware on delivery..

Anyway, cutting a long story short, I (having already done so on the two other machines last year) remved Avast free, and went to install Windows security essentials.

For some reason, Avast did not uninstall, so I downloaded the removal tool - but before I could use it I wanted to go into safe mode. The PC then went through endless recycles and would not start up. I then decided to use the recover disks - but after loading disk 1, the recovery failed at Disk 2.

Anyway, I used the recovery disks from one of the other machines, and the PC is now up and running, after downloading a couple of drivers.

However, after downloading ms Security essentials, a 'Client full installer package failure' occurred, and I could not install MSE. What I then did was pull over a download of it from another PC and that DID install.

Anyway - to the questions: The 'recovered' PC is running and updating (CD key changed to the appropriate windows) - but as for whatever reason the 'correct' recovery disks do not work, there is little point in me backing up this installation -what other options are there?

Can uninstalling Avast (done it plenty times before - not on said machine) - cause the PC not to boot into safe mode/fail to start?

Could the MSE install failure be the download itself, or something else? (again, a new download will not install, but a copy from November 2009 from another machine does install) - it updates OK, and after a couple of attempts, the client update package installed via WUD.