The PSU died and took the motherboard with it.
I feel for you... I mean, I really feel for you! This has occured to me a few times in recent years, ended up spending some cash any buying a PSU that was well made and over specced for the PC... then going a step further and getting a high end fully online rack mount UPS. Since then seen two surges, one of which killed my daughters PSU, but the UPS saved the rest of the equipment down the line from it and even kindy emailed me about the event, best $350 I have ever spent.
I will buy a new motherboard soon. I made a google search and learned that Windows 7 doesn't boot up when the motherboard is changed. So I decided to start salvage of the files today.
Really? Normally when Windows 2K onwards installs it chooses between two HALs, one using ACPI and one without... I would assume windows 7 does similar based on the hardware, I know that it was possible to switch the HAL to get 2K/XP/Vista to boot on different hardware. At a minimum it should be possible to boot into safe mode to recover data from the running system. Obviously this will 'de-activate' windows as the hardware is so different, but it should still allow a few days of use before forcing re-activation.
An alternative option is to source a motherboard from eBay or somewhere else that has the same chipset, this pretty much always works, even with Windows 7.
At a guess (never using Altium) I would say that the data is stored in C:\Users\<YourAccount>\AppData\ somewhere... dig around in there for it. It might be stored in the registry and if so there are ways to get to this data still also, but due to the amount of information stored for an application like this I highly doubt it.