Hi Guys.

I have already read a bunch of threads on this one about other models and tried everything short of sending it away to get fixed or replacing parts. I too share the grief of buying a Sony and forever dealing with problems and incompatibility's.
Anyway, i tried a lot of things with no success. But this post might make a good list of things to try, since i got it from all the other "have to tried this yet?" replies

I have a Sony Vaio tz91(HS), which i bought in Japan and, as it seems, it quite rare in other countries (english manuals? I wish)

The problem
It wont switch on.

what is working
The green light on the side comes o
The battery indicator lights comes on.
The DVD even kicks over in the standard way.
I also managed to carefully open it op and take a look at all the cabling: all fine.
The CPU warms up until the fan kicks in (about 5 mins, nothing strange). Does that rule out the from being fried? (i doubt it)
Its a solid state HD, so I don't know if that is starting.
This is the same effect on mains or battery

what is NOT working
I get nothing on the screen at all. (i checked the cabling too)
I don't even see the infamous VAIO logo come up from the screen
I don't get any system beep
None of the other lights come on (disk drive accesses, keyboard lights, etc)
pressing esc, delete, backspace, f8 repeatedly does nothing. (when it was working, repeated key presses would give system beeps at bootup.)

I have already tried:
battery only, mains only, battery+mains
holding down the on button for 10 seconds. (all above combinations)
leaving it plugging in over night (with battery, without battery)
leaving with with out power over night (without battery)
Removing power and battery and then CMOS battery (its a "ML1220 3V 0907). Holding on for 20 seconds. Then mains on and switching on (got nothing at all then). Replacing CMOS and powering up (back to original problem). Then removing CMOS again (same issue)
There is only 1 ram stick. I have done all of the above with and without the ram inserted.
I also tried an external monitor, just in case

Most likely: what i did wrong
I either switched it off, or put it to standby (cant remember) but didn't check if it actually WENT into that state (ie the green power light goes off). Im running Ubuntu, so i usually check that (due to varying results between kernals)
I was at a friends place and left it on a table indoors. I have since been told that it does get hot there in the morning sun, but cant really verify that it was hot THAT day.
I got up in the afternoon and the green light was still on. It would not come back up. It would not switch of by pressing off, or holding off. Nothing at all. So i pulled the plug and the battery and left it. When I tried to switch it on later that day, I got the above symptoms.

My guess, based on everything i read on this site and others
1. Maybe the CMOS battery is dead:
procedure: replace it an pray (is there more to that procedure?)

2. The CPU is fried.
This machine always felt kinda hot when it was running. I never overclocked it or anything like that.
What is the best way to test this?

Anyway. Im all out of other ideas
Hope the forum can help

Regards David