if the fonts have dissappeared, it suggests they were working not so long ago. that suggests that as others have already suggests you could have a now corrupted version of Access (As Startrekker suggests), or as jmahaffies is inferring your PC has a resources issue.
it could be that you need to reinstall Access. however befofre doing that Id do some investigative work to see if its needed.
It could well be a system resources issue.
think back to what has changed on your computer since it last worked OK.. if you have installed some software it could be an installation problem, where someone or something has overwritten the DLL if you haven't installed software and you have had no disk problems then its almost certainly a software issue. Id try to think what software you have run since the clast bootup sequence and see if you can identify w'what was runing immediately before the problem. Personally Im not a fan of leavign computers (except servers) runnign all day long.. turn em off when you are finished.. there is never (in my books) any good reason to leave it on just in case you want to read email, or in case somebody tries to contact you through facebook or similar. (if you must have the computer on all day long, turn it off at night)..
to diagnose if it is a resources issue...
Boot your PC, with as little running software and devices as possible, just the abosulte minimum you need to run. remove any non critical devices before boot up (thats any USB or other geegaw which requires some support software).
then open up Access.. and access alone + the application you are working on and see if the fault has cleared.. if so you have a resources problem, not an installation problem. if the problem persists check to see what services are running Start | Run and type in msconfig in the box. ***WARNING *** before you make any changes in msconfig, make sure you take copious notes on what you have changed. so if its critical you can re-instate it. for now just look at the services and satrtup items.
A great deal of hardware loads useless software which may make it a leetle bit easier to use or it looks 'KEWL' as opposed to do anything usefull.
another cause for resource issues are memory leaks.. these can be caused by developers such as yourself not closing objects properly in Access, but its also a problem in the commercials world.. graphics intensive software seems to be a real problem (eg programs which manipulate images).
I'd rather be riding on the Tiger 800 or the Norton