Googling on 0xc0000225 yields several boot errors due to a missing or corrupt BCD. BCD stands for boot configuration data. It stores information on how to boot and from which partition.
If that is corrupt then windows will not start. You might be able to repair that if you can boot into repair mode, either via F8 or from a alternative windows install DVD or windows install pen drive.
The first thing to consider is do you really want the HP installation back, or do you want a working windows install. Most vendors install a ton of bloatware. Cleaning them up usually takes a lot of time. Personally I make a backup (just in case) and install a nice clean windows. Activate it, update it and then I make a second backup (to use in case I ever need to reinstall).
Given that your current installation is broken I would get a clean windows image, then
- Wipe the disk clean
- partition it (allowing space for Ubuntu you installing that later does not require any partition magic)
- Install windows, activate and update it.
- Make a backup of this working install (via ghost, Acronis, FOG, windows backup, ...)
Regardless of what you do, getting something which succesfully boots it the first step.
Digital river is a windows reseller which sell clean, legal copies of windows 7. You can download a clean image from here. If you choose a version matching your windows licence on the laptop then you can even activate it. (There is no need to buy a windows licence from them)
Another thing you might want to do is to 'burn' the iso on a USB pen drive and boot that. My experience is that this is much faster then using the DVD, though you loose time transfering it to the pen drive. I consider that worth it if you are going to use that pen drive a few times. A program to do that easily can be downloaded from the Microsoft website here.
Two more points:
- I suspect that the problem is in the BCD store. Read more about how that works here on technet.
- If you are going to play around with that file then easy BCD might come in handy.
If you move the windows iso to a pen drive then you can delete the file ei.cfg. This will allow you to install any version of windows with only one pen drive. You will still need the matching activation key.