Hi Andrew thanks for the wlecome and reply.
The history is that yesterday some nasty virus, turned off my firewall, I got it back on but I think some mare nasty stuff got through, as later I had some error message on googleupdates not being properly installed, then today saw google searches going off to spurious web sites, plus I couldn't run many programmes.
I did mange to get a Hijack log run and also eventually run a malwarebyte programme, which detected several trojan viruses. It was when it asked me to restart the pc to remove a file it couldn't delete, that all the additional programmes started.
I'll be happy to get past the locked XP welcome page and access the log files, to post them in the right forum. But more importantly back up some of my work files.
As I said one step at a time.