I've got an old iMac (about nine years old) which has 2.4 Ghz Intel core 2 duo processor and 2 GB 667 Mhz DDR2 SDRAM). I was running snow leopard and upgraded to El Captain yesterday but the mac is running really slow now and applications such as garage band and iMovie crash constantly. Is there anything I can do? Is it a RAM issue?
You need 4GB of RAM for El Capitan. Do you know what age your Mac is - I'm surprised you were even able to install El Capitan as it seems it must be really old if it only has 2GB RAM! Did you back up first?