ATI Mobility Radeon X1400 Windows 10 driver

http://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_devices/wanting-a-windows-10-video-driver-for-ati-mobility/34ecab17-16a3-4574-a066-56ebeb765122

You may find some help there

for 64 bit windows 10
First, find the hardware lds of microsoft basic display adapter driver

Open settings->system->display->advanced display settings->display adapter properties
On the adapter page, click properties button
On the properties window, go to details
Select the hardward lds entry at click down list
and copy the value, the value is like that
PCI\VEN_1002&DEV_7145&SUBSYS_20031028

Second, Download the 64-bit vista ati x1400 driver from
http://support.lenovo.com/us/en/downloads/ds004138
Extract the package and enter the folder
Packages\Drivers\Display\LH6A_INF
edit CH_49739.inf and find X1400
At the right of all “ATI Mobility Radeon X1400”
replace the hardware lds value with the lds value of microsoft basic display adapter driver that you find at the first step.
save the file.

Third, Install the driver at Disabled driver signature enforcement mode
Open settings->Update & recovery->Recovery->Advanced startup
Click “Restart Now” button then
Select Troubleshoot->Advanced setup->Startup Settings and press Restart
Press 7 number key corresponding to “Disable driver signature enforcement” entry.
After the computer restarted, Open settings->system->display->advanced display settings->display adapter properties
On the driver page, click Update Driver... button
Then select "Browse my computer for driver software"
Next click the browse button at the right of a search box
Find and select the CH_49739.inf file you edited before in the extracted folder 
You will recieve a warning window that warns you the driver is not signed, ignore it and continue

Finally, you installed the ATI X1400 driver and the display is on the full screen reselution mode.

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I "solved" this problem by installing Windows 7 64-bit. If your PC supports 64-bit operation, you will find that Windows 10 upgrades just fine. I did this and now have an Inspiron 9400 running Windows 10 - wicked fast! and the full resolution is available.

I am running a Dell Inspiron 9400 with Win 7 / 64 prof. and 

still get the message that there is no compability with the ATI X1400!

What was the your way to install WIN 10 upgrade?

I was so excited, because I am having the same issues, and this is even the driver .inf file that I need to install. So I followed all these steps, including ignoring the warning, and still the the message that my driver is "not compatible with the current version of Windows." Any other suggestions?

Obviously, I do not have the exact same setup, but am trying to install this exact same driver for an ATI Fire GL V5200 that takes the same driver file (actually, all the stuff that you said to delete and replace is exactly what I needed to leave in there!)

I am running Windows 10 64-bit. I am so extremely frustrated. Windows 10 is updated, Intel has all been updated. Catalyst shows driver is installed. DirectX sees my video card as an ATI AtomBIOS, but device manager still shows an unidentified video controller. After 50+ hours of research, you answer was the closest I had gotten to the exact problem. I just wished it had worked. I will gladly take any other suggestions anyone has at this point. I just want to be able to use both my video ports the way that ATI designed it to be used. That's not too much to ask is it?

Thanks!

good luck and enjoy

Many thanks to KrystinaLuna for for the instruction!

Add:

Don't miss to disable the service "ATI External Event Utility".

This active service requires up to 90% of CPU time.

It works excellent on my Thinkpad T60. :-)