For a single Windows server monitor, you will be able to monitor the following metrics to ensure its continued performance:
CPU utilization - Overall CPU usage, CPU usage by cores, interrupts and context switches
Processor queue length
System idle percentage
Memory utilization - Overall memory usage, swap memory utilization, used memory utilization, memory pages (In/Out/Fault)
Memory break-up - Free physical memory (MB), free swap memory (MB)
Disk idle and busy percentage
Disk usage with capacity plan
Recent events
System statistics including login count, total services running
Top process by CPU and memory
Services and processes - stats on CPU and memory usage, thread and handle count, and the number of instances
Disks - Average and individual disk usage, disk partition details, disk (I/O)
Network stats on data sent and received, input and output traffic, bandwidth, packets sent and received, error packets
Resource Checks - monitor files, directories, event logs, URLs and ports