Additional Study Information: There is considerable evidence that viruses, particularly a virus called herpes simplex, are commonly present in the brains of people with memory problems and may cause or contribute to worsening memory. The widely available and generic anti-viral medication Valacyclovir is FDA approved to treat herpes simplex as it is highly effective against herpes virus infections. This experimental study will test whether Valacyclovir is also helpful in treating memory problems in patients who have tested positive for the herpes virus. You may be eligible to participate if you: Have been experiencing noticeable changes in your memory, language, thinking, behavior, and multitasking abilities, or have been diagnosed with Mild cognitive impairment. Have someone willing to provide information about your condition and progress participation will include: Neurological and physical evaluation by a physician, and cognitive and functional assessments, and brain imaging.