VW Sharan wont start please help

Hi,

I have a VW Sharan 1.9 TDI 1997
Begining of last year I took car to work but didnt start when I finished. Called a friend & he came & had a look & said it was because the oil was low, he put some in left it a while but still wouldnt start. He said to try tow starting it as this would help the oil get round the engine, it started fine with it being towed. Next day started in morn, took it to work again wouldnt start when I finished. Got my sis down & It jump started 1st time. Now as I couldnt rely on the car & weather was warming up I started using my convertible escort so was left for a few months.
When weather was getting colder I took battery off Sharan to charge, put it back on & after about 20 turns it fired up. I moved car up the drive & the electric windows opened by themselves, central locking not working & when I tried turning off the car the key came out but engine was still running, weird! Managed to stop it & it started again ok.
After researching on internet found out Sharans have common faults of the vent near front window getting blocked, water gets in & goes under passenger seat where the electrics r 4 windows, central locking & alarm. And this was the case, soaked up the water & dried it with hairdryer & heater & the electrics seemed fine again.
The next day the car wont start again, turning over several times but nothin. Took battery off again & charged, but turns over but wont start, tried jump starting but just wont fire up.
The car is a little low on diesel would this make a diffence?
Water & oil is fine
When I turn key the oil light flashes several times, is this suppose to?
And the temperature light comes on as well but car is cold, is this suppose to happen?
Not sure the problem not starting before was because of low oil.

Im really desperate for help, im a female but know a little about cars & love to learn more. I dont wanna pay out for someone to come out & have a look as this will be expensive. I would really love to fix it myself not only cos its cheaper but I enjoy it, but losing my patients at mo.

Any help would be very much appreicated
Thanks
Eve