I had a laptop in the other day, a Toshiba running Windows 7.
It was extremely slow to boot up. And when it did eventually boot up, it would freeze solid after about five minutes of use.
I checked it for malware using OTLPE, and I also managed to run TDSSKiller and aswMBR in normal mode before it froze up - I found no rootkits or nasty trojans, just a bit of pretty innocuous adware - i.e. nothing that could cause the slow booting/freezing behavior.
I then ran a full five stage CHKDSK, then I ran SFC, then I checked the registry for missing services etc - I could find nothing wrong with it.
So I assumed it must be hardware related.
I then ran SeaTools, which found no problems. I then ran MemTest, which also found no problems.
At this stage I was pretty stumped. I was thinking maybe motherboard problems or something.
But, just out of curiosity (and maybe a hint of desperation) I then decided to run HDD Regenerator.
Within a couple of minutes HDD Regenerator found (and fixed) a single bad sector right at the beginning of the hard drive. No other bad sectors were found on the hard drive.
After HDD Regenerator had finished I tried booting the laptop. It booted up quickly with no delays and it has been running solidly for two days since then with no freeze ups at all.
So I can only assume that this single bad sector must have been the cause of all the problems.
Seagate and Microsoft are both massive companies. However neither Seagate's SeaTools or Microsoft's CHKDSK could either diagnose or fix that bad sector.
But a tiny little third party utility called HDD Regenerator fixed it almost instantly.
It's easy to see why I was so impressed with it.