Lets separate the issues here:
The problem can be with:
- The hardware.
- The OS core.
- Installed drivers.
- Installed software (both useful stuff or malware)
You can rule out hardware problems by booting another OS. Simply download one of the many liveCDs or their USB pendrive variants and boot from that.
Do the symptoms persist?
If they do that it is not a win8 problem.
If they do not then something on your win8 side is causing problems.
(Note: I recommend doing step 3 and 4 first.)
Discovering if windows 8 somehow has a problem with your OS can be done with a clean installation of windows. Do not install extra drivers. Do not install any programs. Even unplug the network cable. Just install a clean bare win8 from a win8 DVD.
To be more detailed:
If it is the win8 side:
- Get working (tested) windows 8 installation DVD/pendrive.
- Optionally backup your old system.
- Reformat the old drive wiping any possible malware traces. Then do a clean installation.
If the problem persist then it is time to contact Microsoft. However I really doubt that it it. MS bashing is fun, but they actually do a quite good job at testing their OS before it gets released.
On the rare chance that it is slow let it sit there for a few hours. It might be busy with file indexing or rebuilding .dot packages.
And yes, Hours. As in multiple hours. .net stuff can be remarkably slow after an update and I do not know if this also applies to a clean win8 installation. For reference, updating .net 1.1, .net 2 and .net 3 on an old XP installation on a Dell lattitude C (40GB IDE disk, celeron 900MHz) took about 4 hours with maxed out disk and high CPU usage). Needless to say with 512MB the RAM was also full).
Solving 3 & 4
Installed drivers can either work bad or crash. One of the worst cases would be where it crashes as a service and then immediately gets restarted. That would cause high CPU usage. It would not explain high disk IO though.
The same is true for other programs.
To test for this go to the evenviewer (start, run,
eventvwr.msc). Open the [Windows logs[ and check Application and System. If there are errors then please add them to your post.
OK, that leaves a few more things:
Malware: Are you sure that you are not infected? A new system often means a lot of extra programs which get installed. Are all of those from safe sources?
Disk: Are any S.M.A.R.T. errors logged? That should not explain high CPU usage, but it would explain a very slow disk and thus a slow system. Usually this gets detected when a disk has some internal problems, causing it to use all of its time to solve that (rereading the sector until it succeeds, using 100% of the disk time but without much IO).
Memory: 4GB RAM is not much these days and it should be full. Memory which is not in use might as well be in a desktop drawer or still at the shop. Every modern OS is aware of this and uses normally unused memory as a cache, leaving only a little part 'free' for immediate usage. I have no handy link to explain this for windows, but Linux used to use this caching trick before windows did and people paniced. Hence website such as these which explain things. There information is true for both Linux, Windows and other modern OS's