If your late brother put a hint under his password entry box, you might guess at it from that. If he didn't do that and didn't make a password reset disk, you have no choice but to put another Operating System in over the top of Windows 7, wiping it out completely.
A decent Linux OS could be free of charge but Windows 7 could cost you about £80 in the UK - have a look at your local Amazon website.
I've recovered a few using Ophcrack before - Download the Live cd version burn it to a CD and then go into Bios to make sure the System boots from the CD drive first - shut down put the CD in and run it.
If that doesn't work probably will need to reformat\reinstall to get it working.