try deleting the preferences folder, you could just rename the folder 'old prefs' if you like and a new 'prefs' folder will be created automatically next time you boot up. I just solved some major problems with new software conflicts this way, , you probably know all this anyway

my documents/maya/maya 8/prefs

(I have 7 and 8.5 so maybe its created a separate folder for each in my case)

if that doesn't work I;d be thinking 'motherboard.' but some of the other boys here are much better equipped with tech knowledge than me

good luck, I had this happen to me just before the motherboard went, or actually for about 12 months, it just got worse.