hi mick47willis,
Might wish to remove your email addy to prevent unwanted spamming. All help will be given here freely so that info is not really needed.
You can modify your first post so that information is no longer present.
Did your computer completely die, as in will not even turn on? Or it cannot find the operating system and only the vendor start-up page window is displaying? The former means your system is passing the hardware POST test and you have a video display, but the boot hand-off to the operating system is not occurring, possibly because the hard drive died; but the latter means that either POST has failed or or your video card or monitor is dead, or no power from your psu (power supply unit), which would mean no power light would show on the power button.
It is likely a hardware issue that needs to be resolved first before considering whether you need to have your license re-sent to your email address as you need a stable and running system to install and run avast!, or any other program, for that matter.