Here are some good old PC games to have under your belt:
Loom
Return to Zork
Zork: Grand Inquisitor (2000ish old)
The old Monkey Island games
And here are some PC games that should still theoretically work on your PC:
Dungeon Master (1 or 2)
WarCraft2
Evil Genius - a must own classic
OrangeBox
Bioshock
Dawn of War
Galactic Civ 2
Ages of Empires (I haven't played any recent releases if there were any, but the first few are good)
Command and Conquer (any)
Most of the games I mentioned are strategy ones, as a warning.
Edit - Zork: GI may work on today's PC, but I cannot vouch for it.