|""System Idle Process" using 98 - 100% of CPU."|
This is normal and is only telling you the processor is not being used.
Outlook/internet slowness can indicate infection.
Sounds like you are behind on your pc maintenance
Make sure you have updated your antivirus/anti malware and run them
run chkdsk /f at a cmd prompt to check for file table corruption. Answer yes to the question and reboot so it runs.
Uninstall unused programs
Run disk cleanup
Run disk defragmenter.