I have had mild cognitive impairment for months , and now spiked a fever (however cheap themometer say temp is 96). are the two symptoms related ?

Unlikely: If you do not have a reliable thermometer, then you cannot say that you've spiked a fever. Mild cognitive impairment, unless due to an abscess, encephalitis, or meningitis, is not likely to be related to an elevated body temperature. See your physician if your symptoms persist or get worse. You might be referred to a neurologist. http://www.nlm.nih.gov/medlineplus/mildcognitiveimpairment.html