that is a weird one. you did mean outlook express not outlook, right?
Outlook Express/File/Identities/Add New Identity
On the can't create an email, my knee jerk is: can you create a new outlook express identity and try a test email to yourself. If it works then perhaps exporting old inbox into new identity will get you back. maybe your mailbox is getting too large...
On the sometimes blank emails: i wonder if you are having a different issue re: the sometimes blank emails. you might check out your Outlook Express Security settings as Block Potentially Harmful Attachments is on by default now and/or look for message bar at top of your seemingly blank emails announcning attachments blocked for 'security'. you can right-click there and get the attachments. be careful tho. hope you have up to date anti-virus scanning this email before oe gets it...