There is such a big variety of malicious software, viruses, rootkits, backdoors, downloaders, adware, foistware, rogue programs... the list goes on.
It would be impossible to know what your problem is by the description above.
You do have two options, really. You can pay for a technician to look it over, though he would most likely tell you reinstall Vista, or you can get free help at any one of many security forums online.
Many of those forums also have technical rooms, so if it isnt a malware problem you can simply move to another room for a technical expert to assist you, also for free.