So here's the story,
I got a second hand HP tc4200 laptop about 4 months ago had a bit of teething issues, mainly concerning the battery but I got it all sorted out and used it happily for the time I had it. I got used to using the tablet functionality and actually started using it for Photoshop work instead of using my standard Wacom tablet I have connected to my desktop.
May not have been as powerful but I honestly didn't mind.

Now here's my problem, the laptop has now broken down. And now I need help with one of 2 things. Either:

A. I need help fixing the laptop
B. I need help picking a replacement

If you can help with either or these please leave a response. I'll put down the details to each below.

A. Fix the laptop:
The main issue that bars me from easily fixing the laptop is that it is old and second hand. Whenever I got it it was already past warranty and the battery didn't function. So I got a new replacement battery from HP and then it worked like a dream. Today the computer seems to have finally started showing it's age in that it wouldn't turn on properly.

The specific problem is that the light will go on, the fan will power up but the instant that the HP logo appears on the screen (which is always the first thing on the screen) it shuts down again as if it's lost power or something. Then it repeats this process automatically starting itself up and shutting off until I remove the AC. The computer will also not start powering up without the AC adapter even though the adapter can be removed after starting up and ran on battery power alone (at least until the HP logo appears and it shuts off again)

I actually got it to work for a little while, turning off and on as it should (which was good for data retrieval) but the computer has gone back to the continual starting up and shutting off again.

The solutions I've tried are as follows:
I've taken out the ram and cleaned the contacts
I've tried running it on battery power alone
I've tried a different charger
I've tried a different charger without the battery in
I've tried running it without certain pieces of hardware, like the hard drive
(the computer acted the exact same way without the hard drive as it did with)
same with the ram
I would expect the computer should have at least got to some sort of error screen without either of these, but it doesn't even manage that.

If I had to guess I would say it is a problem with power, but I can't be sure.
Any insight or advice would be helpful

B. Replace the Laptop
Seeing as I bought my old laptop for cheap I don't really mind replacing it if I need to. But now I need help finding suitable replacements.
I know there is probably a post that has gone suitable tablet pcs before, but I either cant find it or the ones I do find are old posts and aren't up to date with newer models. If you know any new models or models you have and work with well please leave a response.

These would be my preferences if I could have any:

Firstly I normally use Photoshop and I intend to get the latest version soon so the specs should be at least high enough that I can use that effectively.

I also want to buy it new, so no second hand and no outdated models.

It does need to have a pen and not be purely touch screen.

Finally a laptop style tablet would be preferable. As in rotating fold down screen, physical keyboard, USB jacks, wifi etc.

The one demoed in this video is what I've been considering:
if you have any feedback on it, that would be great.

Thanks guys and gals

(On a side note there, really needs to be a sticky with latest models of tablet pcs or something, it particularly hard to track them all down)