Hi Broni,
I must admit that I am a bot confused by your last post.
When you said Norton I downloaded and attempted to run the Norton Removal Tool. Which is a darned annoying peice of ... software. It appears to start extracting then nothing happens. From previous experience I restarted the computer and tried again, and a similar experience, no apparent action. It appears in Task Manager but says no CPU is being used which suggests to uneducated me that it ain't doing anything. Also I am pretty sure that I did purge it (Symantec) completely before installing Avast, or around that time.
I did the msconfig thing also and, apart from a message from Avast saying I needed to be the Administrator to make those changes (I am the administrator, and XP Home does not offer the option of starting the system as Administrator, except in Safe mode if memory serves me correctly).
I restarted the system and it started normally. I then reversed the msconfig changes.
When you ask "Same problem?" do you mean another lockup? If so I did not get another lock up.
Kind of confused now, where to from here?

Hi Townsbg,
I was replying to Broni when your post hit the site.
I may have got the wrong end of the stick, I thought Silverlight was a development tool. I guess I got that wrong. As a browser add on it is not of much use as I generally don't use IE except for Windows updates.
Re the "thrill" I was referring to once having gotten a boot from the sparkplug of a motorcycle. As this was a kick start machine and the plug was missing the boot lasted only as long as the motor was spinning. But long enough to make me very wary of plug leads. Damn dirty 2 strokes!
And I also said in the same post that whatever plugs into a wall socket I leave to professionals.
I will uninstall Silverlight, for starters.
Then I will reinstall Firefox as you suggest.
As for the RAM, you may be right in that it could be the source of the problem. As I also said in an earlier post can someone equipped with the right equipment to test a PSU also test the RAM? The problem has been intermittnet and if I change the RAM back to the old sticks I won't know for days if I have solved it.
There are two of the sticks, would reversing them be enlightening?

I suppose I misunderstood where you where going with the bike reference.

Some websites have been programed so use Silver light so I'm sure there is a development kit but what they push through auto updates is just something to play those sites. I don't know how it works as I've never studied it. It is also used on FF. If the sticks are mismatched or the new is bad then reversing which slot each is in probably won't help. If you mean stick them in another way, there is only one way that they go in. Ram is tested by memory testing software but I don't know what to recommend on that but if you take it out and you have no problems that is a pretty clear indication that either the sticks are mismatched or the ram is bad.