Try reformatting your PC.
A good thing to do is have two hard drives (for reliability two physical drives are best), but two partitions on the same drive will do. One drive can have your system files on it, the other for data. Back up the data regularly, and create a ghost image of your system drive. When the system goes wrong just re-ghost it.
BVE 4 uses the .net Framework, have you tried installing the latest service packs from Windows Update?
I've not done any extensive testing, but based on my experiences I believe it matters far more what raw processing power you have by having a fast CPU and system bus, than having a good graphics card. It runs well on my laptop with integrated graphics, but not well on my PC with an old CPU but a reasonable graphics card.