How can I get my PC to boot again?

I am no longer able to boot my PC and get a blue screen saying "The digital signature for this file couldn't be verified", along with error code 0xc0000428.

I have tried booting to a USB device in order to access the recovery tools and have tried:

1. Running Startup Repair
2. Running bootrec /fixMBR and /fixBoot in the command prompt which were both completed successfully

3. Running /rebuildBCD in the command prompt which said:

   Total identified Windows installations: 1 [1] C:\Windows Add installation to boot list? Yes(Y)/No(N)/All(A)

   I entered "Y" and the the following message appeared:

   The requested system device cannot be found

However the system still shows the same blue screen. I don't think there are any major issues with the hard drive as I was able to back my files up onto to an external device.

Does anyone have any suggestions as to what I should do next? Are there any more command prompt tests I can try?

Any help would be greatly appreciated.