I have a 1.25 mini that has been running perfect without issue until I upgraded the hard drive and DVD drive last night. I did this upgrade all in one shot and since then it just shuts off. I had a real tough time getting Tiger to install on the new hard drive because of this issue. I really believe its overheating as it feels really hot and it never shuts off cold. I have taken this thing back apart and reinspected everything, including the fan. All seems well and put together. What could be causing this? The upgraded hard drive is a 120 gig Samsung at 5400 RPM. I can hear the fan coming on and staying on after a length of time.