Everything was working up to about 1.5 months ago. What changed then? Can you do a System Restore on your host to roll back to a couple months ago and see if that fixes it?
Alternatively, try a complete uninstall of Virtualbox (not the guests, just the program itself) and your video card drivers. Do a couple reboots to get the host completely used to 640x48 resolution and 4 colors
(You see I remember what Windows ME looked like before drivers were installed). Then put the video card drivers from two months ago on, then Virtualbox. See what happens. If you get everything running, try installing one update at a time, testing your guests each time to see if and when a break happens.
If none of this works, you could have a problem with your video card. Things do break on occasion.
Consider, by the way, not letting updates just happen. I run Virtualbox on an "If it ain't broke don't fix it" basis - only update when I need to, not every time a new update is available. Sometimes the update breaks stuff. Similar with Windows updates, under most conditions wait a week to see if the internet explodes with "Microsoft Breaks 30 Million PCs on Update Tuesday" headlines before letting the updates happen. It saves me some trouble.
I tried everything(except reinstalling Windows) so far and nothing