if the laptop is not switching on. or restarts after 3 - 4 seconds with black screen , most probably your bios is corrupt. Now what you have to do is
1. Open the laptop, take out the motherboard , Find where the bios chip is . ( in acer 5745g there are two bios chips ). you have to pull out the the correct bios chip.
2. Get a copy of of bios file which comes in the form of .bin or .rom extension.
3. Get a Bios Flash Programmer kit.
4. fix the bios on the socket of bios programmer ,run the application of Bios programmer select the chip mentioned on the bios chip u pulled out earlier.
5. select the bios file of your laptop model and . Reflash it.
you can pm me for farther details