Sorted.
Uninstalled Avast.
Copied setup program onto hard drive and installed from there.
Both blue balls appear successively with bubbles and are closed.
Laptop rebooted and problem solved.
Thanks Guys.
Do you mean you copy & paste the contents of avast folder from the CD to harddisk?
It will never work...
No, I installed from the installation program that I had downloaded onto my old desktop computer. Having changed my computer for a laptop Avast was then installed from my CD-ROM of backup files.