LogonUI.exe application error at start-up

[Frrout]

Hi!

(first thing, I haven't spoken english in quite some time, and it's not my mother tongue, so please excuse any mistake)

I've been using my computer with windows 7 for quite some time now, and it never seriously crashed. Except a few days ago: when it's booting, before the welcome screen shows, it crashes during the blue-ish "Windows 7" start-up screen, that blinks instead of booting. I tried leaving it blink, and after some time, it shows an dialog box :
logonUI.exe application error
(RAM error)
the memory could not be written
click OK to terminate the program

If I click OK, the screen blinks endlessly.

My system is installed on an SSD, so I thought maybe my logonui.exe was corrupted, but I can't find a "sane" version : neither on the internet nor on the win7 DVD.

Something that might be interesting: as my SSd is not a big one, I moved many of the folders like my documents and the desktop on another HDD.
I'm here running winXP on another HDD, and it cannot access the HDD where I moved all my stuff, when I could before the bug.
I have a few important files, so I don't really want to format it, so that it could be recognized.

Any idea?

Thanks!

 

[number13]

the report says RAM error, you may have a bad stick of memory, download memtest98, burn to a disk and run it

 

[Frrout]

OK, I checked the RAM, it's clean.
Any idea ?

 

[Frrout]

The HDD with the system files I moved is actually recognized as a GPT partition. Any idea about how to change that back to NTFS, without formatting it?