[DoubleF]

I'd assume the HDD is the original HDD and i's possible the HDD is on its last legs and there are corrupted sectors etc. This could explain the slowness and errors. I don't think it's the mobo unless the computer completely freezes. It's hard to say sight unseen though.

Additional software maintenance to consider are IMO: using CCleaner and using the registry cleanup function to clear out registry issues, deleting old windows restore points/error reporting/temp files/update install backups etc. via disk clean up (built in OS program), software updates of regularly used programs via a program like Avast! smartscan, installing OS updates after figuring out the errors that's stopping it from updating etc. either automatically, or manually.

I reinstalled windows 7 on a computer recently and quite a few things did not work or would not install properly until I installed a specific set up the latest updates. I'm wondering if the issues are partially the same in your scenario.

It's still worth looking into a hybrid drive or SSD upgrade IMO as I'd imagine, age is a factor worth worrying about on the original HDD. Plus, you clone and swap drives first which makes the updates and stuff faster to do/backs up your old drive before you start messing and tweaking the software stuff.