Ok, this happened couple of nights back. I had just switched on my computer and opened my browser when the computer switched off as if power supply was cut. I tried switching it on again but it kept shutting down before windows started loading. The next day (yesterday), however, there was no problem. It ran properly multiple times for a few hours and there were no issues. At night, at about the same time (around 2 AM), it powered off again. Since it was late, I didn't try switching on the system again. Today, it seems to be running fine with no issues. I first thought it was an smps issue. It doesn't look likely now. I thought that it was overheating but that doesn't make sense given the time that the system is shutting down. Any ideas on this weird problem ?