Such a flashing lamp is an indication of a hardware problem, early in the POST (Power On Self Test).
How old is your "Windows 7" computer? Maybe, its motherboard is failing.
Given that Windows 11 will be released in late 2021, think about buying a new computer now, and look for "ready for Windows 11" or "compatible with Windows 11" specifications. You can run Windows 10 now, and then upgrade to Windows 11 sometime in 2022.