Thanks Bryanna and Craig both for your prompt reply and suggestion, I really appreciate it.
However, today I insert the missing USB back to the CPU and it does not work.
CRAIG: the Driver Test file you asked me to run ... I don't know how to run that .exe file on my cpu...can you pls guide me.. Also Yes, I am using a serial cable on this machine . ( I don't know what was that USB for but it was there since I had been running the machine and the moment my software issue arise I took it out and forgot to insert it back, as I said today I insert back again but nothing made a difference).