You have said that you tried cleaning your printer with wet tissue paper. I hope that you weren't using water, window cleaner (such as Windex) or something similar. Anytime that cleaning must be done, one should use rubbing alcohol (aka isopropyl alcohol). Using anything else can be damaging because it will linger in the printer longer instead of evaporating away quickly and that can lead to liquid damage to components that should never get wet, especially if you turn the printer on soon after the cleaning.
At this point, you could have several issues going on. Presuming that one or more parts got wet and thus shorted out when power was applied, you could have a problem with the high-voltage power supply, formatter board, laser unit, fusing assembly, or more. Since you have said that the paper now comes out blank, that indicates to me that there is either no image being drawn on the drum of the toner cartridge and/or there is no charging of the paper occurring when it passes over the charging roller.
To explain, a laser printer operates by charging the drum with the laser. Anywhere that the laser "writes" is positively charged and when the drum spins around, it picks up toner from the inside of the cartridge. While this is happening, the paper passes over that little foam roller (which is the charging roller) and accepts a uniforn negative charge covering the entire surface of the paper. In perfect time, the paper reaches the image drum where the intended image is transferred by the basic physics of electrical attraction. The paper continues through the printer to head to the fusing assembly. This is the hot part of the printer that actually melts the toner (which is nothing more than a very fine plastic powder) and bonds it to the paper.
Given this method of operation, if the laser unit is not working, then the image cannot be written to the drum and therefore there will be no transfer of toner to the drum and subsequently to the paper. If the laser is working but the charging roller is not being properly charged, then the same result of no image is most likely. If the problem is only the fusing assembly, then you would see whatever you printed but you would find that the image was easily removed by wiping it as it was not heated and bonded to the page.
To check whether the laser is working, you can send a test page to the printer and wait for the printer to start pulling the paper through. Once the paper is about halfway through the printing, open the printer and pull out the toner cartridge. There is a little door on the bottom that exposes the drum. See whether there is any toner on it that looks like what you were just trying to print. If so, the laser unit seems to be operational. If not, then you have a problem that will potentially be expensive to fix.
Further, if the image is on the drum but nothing is getting transferred to the paper, that would indicate that something is amiss with the charging roller. This foam roller is very easily compromised by oils from one's skin (let alone any sort of cleaning solution, even rubbing alcohol), so if you tried cleaning this, you probably made your problems worse by making it so that the roller would not hold a charge any longer.
Given the age of the Laserjet 4 series of printers, it is becoming harder to find parts, so while you can spend the money to get it repaired if you wish, I would suggest replacing it with a more modern printer. After all, there are other printers that are faster, more simply designed (meaning fewer parts to fail), and that have cartridges that last just as long (if not longer). As an example, when I finally upgraded from my Laserjet 4M Plus a few years ago, I replaced it with a Samsung ML-3312ND. That printer is just black and white like the Laserjet 4 series, has both USB and Ethernet ports for versatile functionality, and has built-in duplex capability (this allows printing on both sides of the page). The 3312 models have the option of using a cartridge that can print 5000 pages while their cousins, the ML-3712 models, can also use an even larger cartridge that can print 10,000 pages.
I hope all this helps!
HP LaserJet 4...
on Sep 27, 2014