SSD's are not compatible with iMac 21.5in.

Most likely it is Mac-Formatted. Re-Format it in Windows.

Replace the battery. Here's a link to the iFixit guide.

Boot from your install disc and re-install your OS. Update: Here's how to do it. When your computer boots,it will say something like press F1 to enter setup. Then find something like boot order, and use the arrow keys to change the value to optical or dvd drive. Then exit the BIOS and put your install disc in and reboot. Then,follow the on-screen instructions. I don't know what OS your using or I would be able to give you step by step instructions.

Try taking out the disk drive and opening it up. But, that can damage the laser so try taking out the drive and banging it on the table.

You can't upgrade the graphics. The GPU is integrated onto the logic board.

Well,it's your device. But, you might want to try the logic board or battery.