Random Freezes - Video Stop Randomly

I was first using Windows 7 build ~7200, till it ran out of support and I did a fresh install with Windows 7 RTM OEM 64Bit Ultimate. Running it I started expiriencing the bug.

Videos stop randomly for ~1-2mins and get of sync in WMP; Firefox turns to "no reponse" and gets white after I clicked on a link. Clicking on another programm (the mouse is not freezing) makes the program stop to "no response". This also happens to the taskmanager, I've always opened on my second monitor.

After the freeze for ~1-2mins, everything continues normally. I thought something could be buggy with my Installtion and installed another Windows 7 Professional RTM 64Bit. Which I'm running now.

The some sort of this bug already happend without any drivers (running the pure OS), but I'm still not completely sure about it, if it's the same bug. I was sure it would go away with the fresh install and didn't, care I'm sorry.

Another issue:

Running WarCraft3 in windowed mode never took me down to 20fps, which is unplayable, it was ok as I had my new 24'' Monitor and tried to run it in window mode full screen on it to get down to 20-25fps on high grafics, but now it's 15-20fps really laggy on my laptopmonitor, which makes me think about my freeze bug.

Google couldn't help me, installing newest drivers and clean windows didn't help me.

I didn't install new software until that bug appeard, so I guess it's a new driver (because I couldn't find the old ones) or Windows 7 new onboard driver problem.

Memtest86+ ran for more than 8h this night, negative.

I have an other idea: Could it be the harddrive which locks up? Because everything continues normally (like the mouse) taskmanager still shows which process is taking most CPU capacity, but as soon as I perform an action, it locks up/freezes.

The harddrive is as old as the computer, which means about 3 years. What do you think? Could it be the harddrive? Should I try replacing it?