I have dealt with Dell crapware before, especially their incredibly stupidly written restoring program. Before, I had a dual boot system with the Windows bootloader as the primary bootloader (chain-loading grub from the Linux partition), and the Dell crapware did some kind of automatic restore point thing that also involved flashing a fresh version of the Windows bootloader. That had the effect of seemingly making my Linux installation disappear and I couldn't boot to it anymore because of the lost settings in the Windows bootloader. I had to remove all that Dell crapware (which is always a good idea regardless of whether you have a dual boot or not) and reset my bootloader to be able to find my Linux installation again and boot to it. So, I'm just saying that in case that is what happened to you. If not, and you actually restored the system and thus deleting your Linux installation, then there really isn't much you can if you don't have a backup.