Don't worry - the chances are others have had the same problem you're now getting. Some will have posted pleas for help in one of the Mac Usenet newsgroups or mailing lists, and received sound advice and a fix in return. (If you want to do the same, you could start by going to this site's links page).
Wouldn't it be nice if this collective wisdom were gathered together in one place online? Well, that's the idea behind this section of The Mac SE Support Pages. Ever since my SE got on the net I've been clipping these snippets of information against the day when I might need them. So far I haven't ....
However, before you delve deeper, please bear something in mind. I know you're tired of reading those disclaimers that say: "Do this at your own risk, don't blame me if you fry your Mac, yourself, or your entire neighbourhood". But this time it's important. Like I said, I've never yet needed to attempt any of the repairs on the following pages, so can't promise that they will be safe, or even work.
On the other hand, I wouldn't have bothered to clip them if the people giving the advice hadn't sounded as if they knew what they were talking about. But that's no guarantee. Newsgroups aren't infallible, so be aware that all this information is unproven. It may keep your SE from a premature retirement, but be careful.
And if you're one of those helpful people who originally provided this advice and you recognise your own words, I'm sorry I haven't credited your contributions. I began collecting this information long before ordinary people started putting web sites online, and didn't foresee any need to record names or email addresses. Thanks, whoever you are - you make the Mac community the helpful, friendly place it is.
Screen and video problems
Power supply problems
Hard disk problems
Floppy drive & miscellaneous SE problems
Mac SE service manual (pdf, 950k)
Classic Mac Repair Notes, by Thomas H. Lee (pdf, 1.1MB)