imac freezing problems

Basically, the first thing I noticed was (after syncing and charging my ipod) the screen of my ipod had 2 or 3 gray colored lines running across the screen. Lately, I’ve noticed that my desktop iMac periodically has the same lines, (from time to time) when surfing the internet (via Safari). The biggest problem now is opening new window boxes … i.e. opening a itunes, iphoto, or searching my hard drive while I already have Safari open. My iMac would consistently freeze as I was trying to add any jpeg pictures attachments to my Facebook page and while I tried to attach files to emails. The drop down box, which comes down, displaying everything in my hard drive, would (9 times out of 10) freeze midway through … so I could see half the hard drive box. The iMac then needed to be manually restarted, and on occasion it would restart itself. Also, I notice while pulling Youtube or Netflix fullscreen, the screen itself usually freezes or just goes to black and needs to be restarted.

Thanks for the help!