My iMac beep every 5 seconds

Please refer to If your Mac beeps during startup - Apple Support. Please remove and reseat the RAM. If it continues the beeping try changing the RAM DIMMs. If it still beeps your machine has failed, considering it's age I would suggest replacing the machine.

Your welcome.

The reason the SSd will not work in your MBA is because the version of Mac OS that is installed is specific to the iMac's hardware. Mac OS has been like that for over 20 years!

Also, are you saying you never backed up the computer using Time Machine or to create a bootable clone? If you did not then you will need to remove the SSD from the old Mac (or MBA) and put it into an enclosure. The enclosure I recommend is the OWC Mercury Elite Pro 0TB 3.5-inch External Storage Enclosure (macsales.com) Once it is in the enclosure you can migrate from the old drive to the new Mac. To migrate follow the directions in Setup Assistant and Migration Assistant - Apple Community.

You can then use the enclosure and SSD as your Time Machine drive for doing backups. Operating ANY computer without a backup is #1 short sighted, #2 bad computing practice #3 a guarantee you will lose data. Going forward please NEVER EVER operate a computer without a backup!!!! If you are unfamiliar with TM please refer to Back up your Mac with Time Machine - Apple Support

Where did you get the 3rd party RAM modules? If it was other than Crucial.com or OWC (MacSales.com) they will be suspect. Remove them and run with just the Apple modules that came with your Mac and see if you can boot.

If you cannot afford a new iMac, consider buying a new Mac Mini.. You can finance them for up to a year with zero interest and you can have a complete solution including display for about $1000.00. You can use your old keyboard & mouse. A current MM will FAR outperform your 2011 iMac!!!!!!

Another option is to buy an Apple refurbished Mac at www.apple.com and navigate to the bottom of the page and look in the refurbished section. If you go this route only get a Mac with 16GB of RAM or more and the largest SSD you can afford.

If you need to buy a used Mac then please buy from a reputable reseller. NEVER EVER buy from Ebay, they guy advertising in Marketplace, Craigs list, your local PC store. The only reputable reseller I recommend is www.macsales.com

Spending any money on a 12 year old Mac that is worth less than $100 simply does not make sense. If you want to well then okay but take it to an independent Apple Authorized Service Provider. Because your computer is considered vintage and has been for years finding parts may be difficult and expensive.

Best of luck.