Unlike you I'm not 100% convinced the hard disk is the issue, but if you monitored GPU utilization and CPU and they are not the cause of the issue, then it has to be the hard disk. Don't rely too much on Youtube because you can't easily determine if the results are real or fake. You have a weak system with only 3GB of memory which obviously isn't helping; if the OS is swapping (you haven't told us about memory utilization), then additional memory or a SSD would help. My E8400 has no serious performance issues (it obviously is very slow when compared to newer systems), it has 8GB of memory, a 120GB SSD and a HD 5770 GPU. It's OK as an office PC that's used a couple times a month, but it would barely be acceptable as a gaming PC.