I give an update to my post. That was a laptop I ordered for just 10$ and I received it today. It is in perfect condition and was used with great care.
First time I turned it on, it does the same thing you see on the picture. Then I did a reboot (ctrl-alt-del) and the problem didn't come, display worked perfectly. I used it 30 minutes and it worked just great.

So I'm not sure what the problem is. It seems the artifacts appears randomly at any new boot. When the laptop boots without the artifacts, it just works great ... Mmm What could it be ?!?

At the same time I ordered another one (untested and with no power supply) for 5$ ! It came today too.
I plugged the power supply from the good one, and it turns on, but display remains black. On the other hand I haven't had the time to open it and see what's going wrong. Maybe some missing RAM ... I bought this one and the other with the hope I can make one good. But, it seems the first one already goes quite well.

PS : This laptop (ACER 17xx) is just absolutely amazingly incredible. From what I read, this is the only laptop with a 17" screen and a ratio of 4:3. The display is splendid, it is far beyond everything I ever saw for any laptops from the same area. Viewing angles are just exceptional, colors and contrast too. I wouldn't be surprised it is an IPS panel.

You have to see it in person really, this laptop is so huge, it's also the heaviest laptop of the last 20 years. It is more than 15 pounds ! As I said previously, all components inside are the same used in any desktop PC. Real size RAM, real size HDD, real size video card (GeForce FX Go5700 128MB).

It's really the best gaming laptop for the 2000-2005 years !

I'll take some pictures or videos if anybody interested. If you can get that for a few bucks, go ahead !

If the graphical problems disappear after running the machine for a while they are probably caused by a cracked solder joint that reconnects mechanically when the parts heat up and expand.