My system clock somehow reset to a date in 2001 and now Avast says that my license key is invalid & won’t let me update. My trial runs out in July. How do i fix this?
What version of avast are you using Home or Pro?
First reset your system date to show the correct date.
You say trial runs out in July - have you not yet registered?
If not the easiest solution would be to register and you will be sent a registration key - avast! 4 Home Registration
Every boot?
You should check the CMOS battery.
Or, you could be infected, run a full avast scan 
I’ll check the battery, all seems well if I keep the PC plugged into the mains when switched off. I’m using Avast Pro cos I use the PC for business but I’m still working in the red with the new business. Is there no way to get the 60 day trial to give me my full time?
You should email Alwil team (maybe support@avast.com) and tell them the ‘story’ or send them the link of this thread.
This is an antipiracy feature: Trial version can’t be ‘tested’ more than 60 days and it ‘tests’ the clock against reverse backs on the system time.