Question : Problem: Computer won't start all the way. Stuck at Welcome screen.

I tested power supply with a Ultra Power Supply tester and all the lights are on except the -5v l ight.

Does this mean the power supply is bad?

Answer : Problem: Computer won't start all the way. Stuck at Welcome screen.

If it is booting up enough to get to the welcome screen (aka past post) it probably isn't a power issue.

More likely its a driver issue or instability from an abrubt shut down.  Tap the F8 key repeatedly while it boots to get the option to boot into various options.  Try "Last known good configuration" and if that doesn't work try "safe mode" and run CHKDSK when you get in.