Microsoft has apparently issued a fix for ongoing Cortana and Start Menu critical error issues in the form of update KB 3093266. Some users, however, are having trouble installing the update.
I experienced this issue two days ago, and have tried all sorts of fixes along with the powershell command suggested by some forums, but have had no luck, I plan to try this fix tonight to see if it sorts out the issue for me, I spent a lot of time setting up my profile for development, and would be a shame if I have to format my machine or have to create a new profile to get this issue sorted.
Microsoft has let me down again 😦 I am glad that I use a Mac laptop at work. My next personal laptop will be a Mac as well.
After some more research I have come to know that this issue is very much specific to Windows 10 technology preview version, and the version does not automatically update any patches, so what I ended up doing is download the iso for Windows 10 and deployed it on top of the technology preview version and it has sort out the issue for me, I did not loose any data or applications and the upgrade successfully sorted out my Start Menu issue. So it seems that I was to be partly blamed for installing a technology preview version without realising it.
Update 25th October :
The error returned for me even with production release of windows 10, after doing a quick search I came to know that loads of people are stil getting this issue as listed in this discussion, instead of following this workaround I just restarted my machine around three times and on the third time pressed f8 key as suggested on another post, and that sorted out the issue for me for now.