Read about this problem all over the net. Seemed to be caused by a faulty update. Solutions suggested didn't work for me.

Use Windows 10 with two users sharing the same computer. Identical WLM settings except for the mail addresses. Both worked perfectly until few months ago, when with one user WLM froze for minutes every time on starting. The other user - no problem at all.

Tried all google solutions - repaired Live Essentials several times - switched off calendar - etc.

Finally got it sorted a few days ago and it now starts faster than ever, without problems.

What worked with me. Went to the Progs folder (C:\Program Files\Windows Live\Mail).

Found the wlmail.exe file.

Activated the file option for sorting windows compatibility problems (r. Mouse click)

Navigated through the various subsequent windows and told the machine that Windows 7 used to work and to use that modus.

Now works perfectly. Might help someone as frustrated as I was.