This was reported by a user on Windows Central. “Do those dealing with this problem have avast antivirus installed? If so, I believe that is what is causing the ‘critical error’. I uninstalled the software and upon reboot my start button and cortana were working perfectly again.”
If this is correct then Avast will need updates soon. If not an Avast issue then Windows Central need to be informed.
No problems with start or Cortana here
I had that issue alot with older Avast versions and Insider builds, but not recently anymore 
Im facing this issue 
and I have try all the steps from Windows support page , but nothing works , and I see most of the users with issues has Avast installed , is there any help for this here, also after update to Windows 10 I notice the firewall from Avast didn’t works :o
Repair Avast:
- Control Panel → Add/Remove programs → Avast
- Click on ‘Repair’.
- Follow instructions.
- Reboot.
i am having the exact same problem in my 3 computers running windows 10 with Avast internet security.
yes, Avast is updated to the latest version, windows 10 was running fine for the last 10 days.
what gives??? good quality control avast…
7 days left on my license, i am glad this happened today.
I’m having this problem as well, start and some task bar icons don’t work.
Windows defender is greyed out.
Also can’t find avast in control panel/programs to carry out a repair or uninstall n re-install.
Also Avast updates are hanging. I’ve also sent 2 notices via the app regarding this issue with no response
I had this problem and also, even if I don’t get the critical error, the whole Windows 10 UI freezes. I have to use the task manager to restart the explorer.exe and than bang!! Same thing happens… Sometimes I get the Start & Cortana Critical Error if I wait long enough.
I had to switch to another antivirus because of this.
It is not avast related on. Just had this one from nowhere first time on Windows 10 after one month. Just restarted my PC once and error is gone.
Fighting this issue for 3 days now (and I’m an experienced break/fix tech)
You can try system restore, but in order to do that your going to have to completely uninstall avast! and reboot first (make sure you reboot). For whatever reason, even with the SDM turned off, system restore isn’t able to modify the definitions folder for avast! and will fail.
My first system restore has brought back Cortana, but I still don’t have a start menu.
As far a rebooting to fix… I’m sorry to say that you are only at the beginning of the problem my friend. It started out like that for me too. Reboot/Logout would fix it every time. Then, a few days later… start & cortana are both completely unresponsive.
When I figure it out, I’ll post
Sadly, but It’s true. Still it’s a fact! I’ll wait some resolution of this matter.
I had to reboot my system several times to get this cleared up.
Sorry, I don’t buy into the thinking it’s an avast issue. I do believe in
making regular system backups. At least twice a month preferably once a week.
An aggressive backup program is a must. There are several backup utilities available,
personally I use AOMEI Backupper Free. To be honest I’m making a backup right now.
This is not Avast related as it has been around since the beginning of the year http://www.bidnessetc.com/49429-microsoft-windows-10-start-menu-cortana-taskbar-not-working-heres-fix/
http://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_cortana/problem-with-cortana-and-the-start-button-on-build/f21076b4-254e-43fe-a3e9-ebb890e61c0d?auth=1
https://www.reddit.com/r/Windows10/comments/3fq8k3/windows_10_start_menu_isnt_responding_accurately/
plus a few hundred more
Most whittle the problem down to windows search
It seems to me the culprit is Cortana. IMHO Cortana is something that is totally not necessary and Microsoft should dump it.
The main problem might be that the entire so called “modern apps” environment in some cases can’t be properly initialized or crashes. I would say that errors regarding Cortana and Start menu are nothing but “side effect”.
I don’t wish to argue with anybody who is responsible about this issue, but:
- fact - with the avast av I have the issue, w\o - haven’t!
- it isn’t interesting how or why, as user (in case of Avast & Microsoft) what is important for me is WORKING SYSTEM!
Frankly, the MS isn’t the big losing of this
May be MS is responsible, there is such possibility for sure!
I wish successful resolution of this matter!
I also just installed Avast Business and immediately had this Start Menu Critical Error failure appear .
I can reboot and it will work for a while but next reboot it fails again.
Note: Please don’t reply or give opinion if you are NOT running Windows 10. it’s not helpful.
many reports of this found in Google. the solution is usually removing Avast. anyone found a different specific fix to make Avast stable on Win 10?
about:
« Reply #18 on: Today at 07:21:41 PM »
Unfortunately it’s “definitely” not “usually”!
For now I don’t know any kind of “work-around”. And more, the time spending for pointless searching
is much more expensive than the particular av-software
There other AVs working fine with w10! In yours case “Avast Business” it means some money
But as i said above, time & security are most important, so find another way!
Obviously AVAST trying to prove that the cause is in MS (it’s their right & business:)
I wish you success