The next step would be opening up the case. If you are not comfortable in doing this than a repair shop is probably your best option.
If you want to try yourself either your manual or an online guide should show you how to open it if it is not obvious.
Most manufacturers have manuals online at their web sites.
In opening the case the most important factor is preventing static electricity as seen here:
ESD - What can I do to avoid damage
Once open you will see a disk battery like a watch or camera battery. Remove this. Look in the same vicinity for a 3 pin jumper block that will probably be labeled JBAT.
If it is there there should be a plastic sleeve covering pins 1&2. Switch this to pins 2&3 and wait a few minutes. Then return the jumper to 1&2 and replace the battery and try to reboot.
This will clear all the motherboard settings. You will need to reset the Time etc. if all goes well.