This often happens during a storm and usually is quite an easy fix.
Remove the power cord, from the back of the computer, with the back of the computer facing towards you, on the right hand side there should be 2 screws top and bottom, remove these screws and take off the side panel.
Inside the case, on the motherboard you will see a large battery, take that battery out and leave it out for 30 minutes.
Now, remove the system memory, the memory will look like this >>>>>
Just unclip the memory, get a clean, dry, soft paintbrush and clean the brass contacts on the memory with that.
If there is any dust on the slots that you took the memory out of clean them also.
Wait for 30 minutes, reinsert the memory making sure it clips into place properly, put back the battery, the side panel, the power cord and power the machine on.
When the system boots up you will get a CMOS error, don't worry about that just go into the BIOS and set the time and date, save the changes and exit the bios, the computer will restart and hopefully boot into Windows.
If you need anymore advice please post back.