Problems with Mozilla Firefox Thunderbird account. Documents now inaccessible. I can't complete my work. Real crisis. Finishing book - publication due.

Microsoft seems to have interfered with my computer. I have been using it for 10 years using Mozilla Firefox with no problems. Now all my own documents have been frozen and I am unable to make any alterations or continuation of text. I am desperately worried. I am 83 years old and started using computers relatively late in life. I am a complete 'generational novice'. It seems as if Microsoft has had some input. Please help