I think so as well, but one month does not fit into that category.
It's a matter of opinion, really.
Regardless, as bononos mentioned, it was probably some form of malware. This has has been my experience, as someone who fixes computers for a living. The OP apparently ran a single scan, which simply isn't enough to rule out an infection. Bitdefender (which is what IObit uses) is fairly good, but nothing is 100%.
My big 3 for infection cleanup are HitmanPro, MBAM, and ESET Online Scanner. Those usually get most of everything. If those three don't find anything, you're
probably clean.
Occasionally something new will come out that bypasses scanners, and running msconfig and cleaning up your startup programs and services is a handy tool. chkdsk with /r and /f, and sfc would be another thing I would try. Although the OP certainly wasn't experiencing this issue given the crashes, sometimes CPUs get pinned at ~100% because the power settings are messed up and the processor is running at a sub-optimal frequency.
Last but not least, there's the backup and reinstall option. The OP seems to have done something similar by upgrading to Windows 7.
This list is far from exhaustive, but it's a good start. I can't imagine this being being anything but a software issue.