In other words, you had a warning that something was wrong and nyou ndecided to try Windows 8. In general, installing a new OS is not the best way to isolate a possible hardware issue.
Frankly, the best recommendation is to get another hard drive and try to install the same OS you had before. It does not have to be a new drive, just one that works. The failure rate of Hard drives is not easy to determine. Sometimes they go for years. When you system slows down, that is often a sign of coming HDD failure.
A quick check on eBay has Fujitsu 120 GB Internal 5400 RPM,2.5" for about $20 and come with a 14 day return policy. That is a whole lot cheaper than going to a local technician, if you live in California.