Please refer to this article for tips on troubleshooting a slow computer: http://en.community.dell.com/wikis/spyware_virus/computer-and-browser-slowness-malware.aspx
If you have tried all that and you still have a problem with slowness, it might be good to post a log.
Logs are read on the Malware Removal Forum.
Please Read This Before Posting For Malware Removal Help
Microsoft MVP - Consumer SecuritySocial Media and Community ProfessionalSpywareHammer
I am not a Microsoft or a Dell employee. I am a volunteer.
These links might help:
Slow Computer? Use this troubleshooting checklist
Help! My computer is slow!
Dell Forum Member since 2,000
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I'm not sure if pc health advisor can help you, but try to refer them. I am too had problem like this before and I just refer to pc health advisor, they have step given to help your pc speed.
The vendor for PC Health Advisor is ParetoLogic.
My Web Of Trust security does not give the vendor site such a good rating: http://www.mywot.com/en/scorecard/www.paretologic.com