Bluetooth on imac suddenly stopped working

Question

To start, thank you for reading this question with the intent to help.  My imac LionOSX 10.7.5 .  Does anyone have experience or knowledge about how the bluetooth to a computer can suddenly stop working.  It happened at the same time that the computer start up slowed way down (Just took 4 minutes...i timed it so I could know for sure).  It used to start up in about 30 seconds or less. (The computer itself seems to work as fast as normal once the start process has finished.
At first, I thought there was something wrong with my keyboard and mouse, but couldn't even log in to access the system preferences, as both were not working.  So I grabbed an old keyboard and mouse from my Windows desktop, plugged them in and was able to log in.  That is when I noticed that the bluetooth icon in the menu at the top right of the screen showed a line through the bluetooth icon and when I click on it, it says "bluetooth unavailable.  When I click on the "About this Mac"/more info and look under bluetooth, it says "no information found".  Also, the mouse I plugged in stopped working the next day until i plugged it into a different USB port.
My fear is that I accidentally downloaded some kind of malware that is eating up different functionalities on my computer.  I did use a web-service to download a youtube video on neck exercises (how stupid of me...could have simply bookmarked it and pulled it up just as easily)
If you can help, I would be oh, so grateful.  I know my way around computers in the most basic sense, but don't understand much about the how's, why's, how-to's of computer technology.
Thanks.  Your friend, Patti P

Answer 1

Sorry I haven't gotten back with those of you sooner about your suggestions and how they have been working. Tried one day, but the site was down due to maintenance. 
I have been trying all the wonderful suggestions people have given, but so far with no luck.  It is absolutely clear that the problem is with the internal bluetooth and not with the keyboard or mouse.  I bought an external bluetooth usb adaptor, and now my bluetooth devices are usable again, but the internal bluetooth is still unavailable. Thanks for letting me know that the long wait at startup was more than likely due to the system searching for the bluetooth, very comforting.
In one article I read, the person recommended trashing the plist file, com.apple.bluetooth.plist, but I couldn't find a file like this in the library.  However, I did find a file named 'com.apple.Bluetooth.Audio.plist' which was modified on June 12, which is the same time the bluetooth stopped working. I don't know what to do with this file, since I really know nothing about how computers work, code, etc., etc.  I just really enjoy the finished product, so to speak.  But here is what I found when I opened the plist file.
Here is the first entry:
Root: previous input UID    Dictionary: string   Value: AppleHDAEngingInput:18,0,1,0:1
When I clicked on and opted to copy, this is what pasted when I pasted it: <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<string>AppleHDAEngineInput:1B,0,1,0:1</string>
</plist>
There is a 2nd entry:
Key/Root: previous output UID   Type/Dictionary: string  Value: AppleHDAEngineOutput: 18,0,1,2:0
When I copied and pasted this string (or whatever it is called…it's all greek (or perhaps I should say geek) to me, here's what pasted:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<string>AppleHDAEngineOutput:1B,0,1,2:0</string>
</plist>
I also found two files that were logs of events that occurred on the 12th and 13th.  I have copied and pasted this info and put it into two text docs, which if I can figure out how, I will attach in case someone is able to look at code and figure out what it means.  That is way beyond me (and I envy those who can read this foreign language)
In addition, there is a folder named 'com.apple.BluetoothFileExchange.savedState' which was created on June 12th also.  It has 2 documents, one named 'data.data' and another named 'windows.plist'  I took a screenshot of the plist file which i hope I can include somehow in this post.
There is a 2nd folder created June 23 named com.apple.BluetoothSetupAssistant.savedState that has a data.data file and another windows.plist
These are the only files/folders that came up when searching the library under the key word bluetooth. 
Thanks to everyone who was so willing to help.  While I wasn't able to fix the problem, I learned lots of good stuff, like how to find my library, etc. so just know your efforts to help were not in vain. 
Your (grateful) friend, Patti P