You have been sold an infected computer that's running an obsolete operating system. Whatever you paid for this system, it was too much. If possible, I would advise you to exercise your best option, e.g., return the computer to the party from which you purchased it and get a refund. The seller most assuredly knew the system was both infected and obsolete.
Microsoft no longer supports Windows 98, and there are very few software products and/or malware removal tools available that will even run on that operating system. It isn't worth keeping and it certainly isn't worth spending additional money in what would be a futile attempt to upgrade the system, so don't let anyone talk you into throwing good money after bad.
Having been apprised of the status of Windows 98, if you still wish to attempt cleaning the system of malware, you will need to post a HijackThis log.
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In order for us to help you it is necessary that you provide us with a HijackThis log. Please follow the guideline at the link below to start a new topic and post your HijackThis log by pasting it into your post. Do not utilize attachments. This topic is now closed. Please start a new topic by following the HijackThis Guideline posted here: >Guideline for posting your HijackThis log<