IF it's a laptop, replace the battery, reconnect the AC power and power it up and leave it alone for a while. NO other devices, no USB dongles for anything (wireless network, wireless keyboard, wireless mouse), no printers, no Ethernet connection, nothing but the bare minimum basics. In that condition, press and hold the power button for 30 seconds. My standard non-techie response would be to turn off the computer, disconnect it from AC power, if it is a laptop remove the battery. On the upside it apparently boots and what you refer to as a 'screen saver' which I suspect is the lock screen cannot be dismissed by striking the space bar or by a mouse gesture would seem to indicate that neither of your two input devices are working.
Manufacturer Name, Model Name, Model Number
Some details as to 'my PC' might be helpful.
Click to expand.That makes things difficult and it may be that you will need to seek professional help in resolving your problem, unless you have a more tech savvy friend, relative, neighbor or someone else in your social circle that you might be able to call on.
