system busy/ unstable

[vetman]

My laptop is drivin me crazy!!! If the system is left on for sometime (couple of minutes) and not being used, normally the screensaver comes on or it goes on auto. standby. However, when i want to resume using it, the system moves ridiculously slow and often times a message about system unstable/ busy comes up. This has been a relatively new occurrence and i have not added prog. or software recently, except for some micros. critical updates. Available system resources are ok and there is no evidence of viruses or spyware or adware. What do u guys think?
Thankz . Awaitng ure response.