Bluish screen -

is it a greenish blue?..... if so you have lost your red signal..... check your monitor connectors for bent or broken pins...... usually happens after swapping cables or monitors on a computer..... you could also have a bad cable or monitor.....

is the monitor a CRT or a flat panel.... loss of one color is very common on CRT monitors, and could be a bad solder connection on the CRT driver board, or a bad video chip..... flat panel LCD monitors don't usually lose a color, although it is possible.... the most common failures on LCD flat panels is total power supply failure (no power at all) or display matrix driver failure (colored stripes across or down the screen), but a cable failure is also possible, like i said above, check the connectors for bent or broken pins..... there are 3 rows of pins...... at the widest side of the connector, there should be at least 3 pins next to each other on that row (sometimes there are 5), the middle row should at least have 3 consecutive pins as well (and again, there are sometimes 5)
the last row (the smaller side of the connector) should have at least two (but sometimes all 5) pins in it. the first row and last row of pins should line up vertically, and the middle row is offset a half a space, so from top to bottom, the columns of pins make a zigzag...... if the connectors are alright, then your most likely problem is the monitor..... if another monitor works on the computer, it's the monitor..... if another monitor has the same problem on this computer, then it is the video card (or the motherboard's video output, which is fixable by installing a video card)