What should i do for my sick pc?

frm many days pc shwing problem.....my pc was encountered with virus so i format my pc bcs antivirus was fail' 2 solve this problem.........after i install wiindow n also before installing whn pc suffered virus , my pc shwing problem..it's running on lowest color 4bit...whn i adjust highest 32 bit n after click on yes,it's again running lowest bit..i try this many times but again it's running on lowest color......n on pc screen there r up 2 down lines shwng n screen is looks like pixelate,too much big icons............whn i install window thn in starting whn intel icon n page shw it's looking clear bt as normal screen bt cd start booting it's again shwing this low bit n pixel,lines problem n in left side of screen in down a mark is shwng as like wave diagram..whn i tell this problem 2 my frnd who is eng' in hardware...he told me tht acc. 2 him it's nt any hardware problem like cpu....he told me tht in back of monitor there is a screw who is for pixel'......he told me tht may be tht screw is loose thts why my pc is nt supporting pixel,whn tht screw 'll tide, pc'll be fine.........n it's nt windows cd problem bcs i try win7,win xp..............n it's shwng in every os................so wht should i do???????????any solution?????