Error C1900204 indicates that the Windows Upgrade has failed; this error is most recently related to the windows 10 upgrades. There can be several reasons why the update is failing; to be more specific you can check the logs file called setupact.log from C:\Windows
The setupact.log file contains the specific details of the error why it is failing. You can troubleshoot the error if you understand it; or post the error details on http://equestions.net/ ask for more specific help.
The aim of this guide is to address this issue by creating a bootable iso image of Windows 10 or upgrade it using the media creation tool. However, before you do that make sure you create recovery discs for your existing operating system or take a full back up in case you need to revert to previous operating system.
Assuming you now have the required back ups; follow steps below to attempt upgrade first. If that fails; you can do a clean install via the iso.
If you clean install windows 10; you will be required to activate Windows 10 using the key.
Before proceeding with the upgrade/clean install please do a compatibility test to ensure that the hardware can support Windows 10.
To do the compatibility test; follow these steps below
1. Click on the Get Windows 10 icon from the taskbar to open it up.
2. Click the 3 lined bars in the top left corner.
3. Click on Check your PC to scan and test/check compatibility.
If all is well and the hardware is compatible; proceed with the steps below otherwise it is better in my opinion to stick to what you have or if you can upgrade the required hardware first; you can then proceed with the steps again.
BUT the cost of purchasing and configuring the hardware may exceed the cost of getting a new computer/laptop with Windows 10 already on it.
Upgrade Using Media Creation Tool
2. Scroll down to the bottom and locate the correct system type version for your processor type. (32 bit or 64 bit).
3. Once you run the tool; you will be presented with two options.
a) Upgrade this PC Now
b) OR Create installation media for another PC
c). Choose the Upgrade this option now and proceed with the steps on screen. This option has worked for most of the users who were getting the C1900204 error.
If you wish to Clean Install Windows 10 follow the steps here