Pc switches itself off

Hi I bought a new galaxy 3 pc case last week
PC seemed ok but temp was too high 90oc on desktop then when on idle for an hour pc switched itself off. On bios cpu temp was 60oc which was too high my cpu is amd athon 3200+ socket 754 Winfast Foxconn micro atx motherboard I've cleaned out the pc for dust including the heatsink the temp in cpu was still too high 93oc, no thermal paste has been put in for a long time and the rear fan from my old pc case doesn't work. What do you suggest I do? I doubt it's my new pc case causing temp issues but I do think it's the cpu as pc has switched itself off after an hour even on idle. My power supply is
atx 500w I've had that about 3-4 years pc powers up ok on loading just on desktop it switches itself off after an hour. I've got speed fan on my pc to tell me what cpu temp is and it's come up in the 90s I also have core temp which has said the same thing. I have 512mb memory and another ram which makes it 1ghz and sound card realtek97 i've not been on pc recently as it'll switch itself off and I dont want the lifespan of my pc to be short so I'm being careful but I do need better fans and for the rear as well. Any advice would be appreciated thank you.