Q: iMac desktop has freaked out

My parents have recently had problems with their IMac and wanted to completely reboot it although needed to back up their info and while I was given a backup external drive, i tried to transfer the information but about 1 thousand pictures went into the the desktop instead. Ever since this happened the computer cannot function in the least bit. The response is delayed but minimum a few minutes and nothing is working. I can't open many applications or it ignores my request. No matter how many times I restart the computer or leave it, it just stays put the way it is. Is there any way I can delete this info so it stops freaking out?

Thanks!