When i turn on my 4520, all the led's, i.e. HDD,

has happened to me before- remove power cord, remove battery. flip laptop over, look for removable covers for memory (ram), hard drive, motherboard. you can either slide the covers off, or they have a phillips head screw (+) holding them down- you'll need a small one for this! don't lose the screws! first touch metal (lamp, pipe, whatever, to discharge static electricity from your body!) OR YOU COULD FRY SOMETHING! start with the ram sticks, they should flip up, then have a little hold-down on either end- spread (gently!) the hold downs and release the chip- then re-seat it. if there are 2, then repeat with 2nd chip. lock chips back in place (push them back down until they lock into place- parallel with the bottom of the laptop- replace cover.
next, after touching metal again, take the cover off of the hdd enclosure- see if you can release it and reseat it. you may not be able to without removing a bunch of screws- anyway, try making sure it is well seated! replace cover.
next, if you can (touch metal first!), remove cover from motherboard enclosure. examine how it's connected to the rest of the circuitry. if it plugs in, remove hold down screws- slide it out a little, and re-seat it. look for any areas that may have lost their 'smoke' (burnt, or discolored areas) see these and your mobo is probably shot! if your hdd is still good, your data is still there! you may have to replace the mobo, or get another laptop that can access your hdd, so you can re-access your data.
re-secure your mobo, and replace cover. replace battery, power cord, and try re-booting!!
no guarantees! can only try!
good luck!

My acer aspire 4520 Will not come on

remove your battery for about 15-20 mins. plug back in and try. If same thing occurs there may be issues with your motherboard.