Six year old with behaviour problems.....help

[GlastonburyGoddess]

Posting this again as I forgot to add a title.

My 6 yr old ds1 has behaviour problems(not yet known wether underlying problem exsists-under paed) and has good weeks and bad weeks, its like a rollercoaster-he'll have a reasonably good few days, then he'll have a run of horrendous days where you cant do anything with him.
He doesnt respond to sticker charts or anything along that line and time out seems to have limited effect.

He was at home with me today as dp at work and ds2 nursery. he was fairly good all day, until I realised he had scratched the LCD screen on the tv-not a bit, but all over big deep scratches. Im pulling me hair out about him, He must have thought about doing it, sneaked in the kitchen and got a knife or similar and then did it-its not like there was something by the tv that he just picked up and used, it was premeditated.

I could sort of understand it if we had had a arguement/disagreement, but as I say there was no reason for him to act like this.

Anybody else have a child this age like this-how do you cope?

what would be a suitable punishment for this in your opinion?
Any comments/advice etc welcome

Anyone.......?

bumping for you as no clue.

I remember deliberately colouring in the wallpaper in my bedroom around the age of 7 because I was curious about how it would feel to do and how it would look. Nowt wrong with me

Thanks, Im at my wits end tbh as its so often that something gets broken/ruined. Mostly I can see above it but when it concerns expensive items that we have no way of replacing/claiming on, it makes me want to cry.

Yes my 4 year old (who is at school and knows far better) drew on our dining chairs a few months ago, and the table cloth in biro and probably various other stuff that I'm choosing not to remember. It makes me want to cry too, we've not got much valuable but it's not the point is it - very very annoying.