Hi 
If something worked and suddenly stopped working as if by magic then
the first thing to try is to rename your User Profile
https://wiki.documentfoundation.org/UserProfile
Renaming is better than deleting because you might have tons of stuff
in your profile (templates, galleries, Extensions, file-backups etc)
that you don't want to lose. If renaming or deleting the User Profile
DOES work then you might be able to copy chunks of your old one back
and that can be a good way of trouble-shooting down to pin-point the
problem. If you have deleted the User Profile then that is, of
course, impossible. If you just renamed the User Profile then you can
leave the trouble-shooting to a day when you do find time (or never
but at least it's possible). If renaming DOES NOT help then you could
rename the old one back without suffering any losses.
On the other hand it is quite possible that you don't have anything
exciting in your User Profile or that it might be a good time to start
afresh with reconfiguring LO's settings and with installing fresh
Extensions that you need now rather than trying to keep using ancient
ones or ancient versions of ones you don't really use any more.
If the problems happened straight after upgrading to a newer version
then reverting to an older version makes a LOT of sense. Preferably
an x.x.4 or higher. It's that 3rd digit that shows greater stability.
The 4.1.4 should be about as solid as they get but some people are on
4.0.6 to get the extra stability of that although they miss out a lot
on features and compatibility with MS formats. Although i have some
machines still on 3.5.(something) without really missing anything but
then my needs are modest for those machines. Anyway, 4.1.4 is a good
release and it's worth carrying on following the 4.1.x branch as it
gets developed further and stability increases further.
However 30+ worksheets in a single file and 1Mb means it's quite a
huge file! If you can't break it up easily (or even if you can but
don't want to) then it is well worth considering using a specialist
spreadsheeting program instead of Calc/Excel. Both the later are
designed to integrate well with other modules/programs within an
office suite but means you are carrying extra baggage and your
computer is using resources to make it easy to switch into
Presentations, Drawing programs, and all sorts of stuff that you
probably don't need while using the spreadsheet. A specialist tool
focussing resources on, and designed purely for handling, spreadsheets
might be better.
Gnumeric uses the same formats as Calc natively and can also handle
the relevant MS formats and is often found to out-perform Excel and
even Calc especially on low spec. machines.
http://projects.gnome.org/gnumeric
From their News section the quick link to directly download their
latest Windows version is
http://people.gnome.org/~mortenw/gnumeric/gnumeric-1.12.9-20131128.exe
NOTE this directly downloads an Exe file!!! I NEVER usually give
links like that because you don't know me and have no reason to trust
me so you really should try the first link and have a look around for
yourself before attempting any downloading! The only reason i give it
this time is because i found it difficult to find on their site so i
just wanted to make it easier for you.
Regards from
Tom 