Hello, so yesterday I got onto my Dell Inspiron 5755 and a red box popped up saying "Secure Boot Violation, Invalid Signature Detected. Check Secure Boot Policy in Setup" I click okay and my laptop tries to diagnose the issue with Dell Assistant but says that nothing is wrong. I tried disabling Secure Boot and it did get rid of the red box but my laptop still will not start and tries to diagnose the issue. I have not recently updated my computer at all so I don't know what it could be. I'm mostly worried that if it's some kind of virus it'll get information from my web browser but otherwise there isn't much on my computer. I've also heard it could be my hard drive but I don't know how to tell. I wish I could give more information on my laptop but I only know that its an Inspiron 5755 with a 17 inch screen. Thank you in advance for any help!
Unless you're trying to run Windows 7 or some version of Linux that doesn't support Secure Boot, if this happened all of a sudden, then your bootloader has either been corrupted or maliciously altered. If you go into the BIOS and disable Secure Boot and then your system seems to boot normally, then chances are you've been infected with some sort of rootkit. If you disable Secure Boot and it still doesn't work, then it's possible some sort of Windows update went haywire. Either way, unless you happen to have been capturing image backups of your entire system, you'll need to reinstall Windows from scratch or recover from a factory installation image if one is available for your system either already on the drive in a recovery partition or available via download if you can get to another PC to download it and create a bootable flash drive.
Going forward, you may want to consider capturing image backups of your system as protection from things like malware issues and Windows updates gone awry. Macrium Reflect is a popular tool for this purpose and is available in both free and paid versions. The free version is entirely adequate for periodic "lifeboat" system backups for this purpose, although if you decide to rely on it as a full data backup solution, the paid version has some features that you may find useful.
Sorry to hear about this!