It's hard to determine without trying other 1080p devices. The issue could be the cable, or how the signal is being sent. Since it works in a store, it definitely may be worth investigating further, particularly since you're still within warranty.
I would recommend having your unit inspected, and if something is wrong, it can be addressed by a service technician.
I wish I had some tips, but there's not a lot of variables we can test with one game console. Changing the cable might be worth a shot, and I would try that before having it inspected.
I'm currently having a very annoying problem. Here is how it goes, i have hooked up my PS3 to my TV, which is new it is a samsung UA40C5000 (40" Full HD etc.) and it works mighty fine under the 526p resolution (or what ever that 500 number exactly is) And no problems at this resolution.
I then change the resolution to 1080p and it looks wonderful but then after 10 minutes or so (longer at times) the signal shown is a horizontal line of pink dots and then "mode not supported" even though the PS3 is still on. I can turn off the PS3 and wait about 30 minutes and do the same thing again, it seems to always work for a short time then dies out. I can alternatively hold the PS3 button down to reset it back to the default 526p setting which works.
I have also tried this on the 1080i setting and the same thing happens.
I initially thought it was the PS3 but upon taking it back to the store, the store mangers could easily play on 1080p resolution for a long time with no glitches, as well as 720p and the other setting.
The question i have is what can be causing this problem? Could this be a case of the HDMI cable? What is curious is that this is a temporal thing that it lasts for a short time before it dies out, whether the PS3 is on idle (settings menu) or in a game at a high resolution.
Which measures can i take to fully diagnose and fix this problem? I dont have any other devices that can show 1080p HDMI connection
TV: samsung UA40C5000
PS3 160GB slimline
HDMI cable: Belkin 1.3 compliant cable